COMPARISON OF LOW COST PHOTOGRAMMETRIC SURVEY WITH TLS AND LEICA PEGASUS BACKPACK 3D MODELS

This paper considers Leica backpack and photogrammetric surveys of a mediaeval bastion in Padua, Italy. Furhtermore, terrestrial laser scanning (TLS) survey is considered in order to provide a state of the art reconstruction of the bastion. Despite control points are typically used to avoid deformations in photogrammetric surveys and ensure correct scaling of the reconstruction, in this paper a different approach is considered: this work is part of a project aiming at the development of a system exploiting ultra-wide band (UWB) devices to provide correct scaling of the reconstruction. In particular, low cost Pozyx UWB devices are used to estimate camera positions during image acquisitions. Then, in order to obtain a metric reconstruction, scale factor in the photogrammetric survey is estimated by comparing camera positions obtained from UWB measurements with those obtained from photogrammetric reconstruction. Compared with the TLS survey, the considered photogrammetric model of the bastion results in a RMSE of 21.9cm, average error 13.4cm, and standard deviation 13.5cm. Excluding the final part of the bastion left wing, where the presence of several poles make reconstruction more difficult, (RMSE) fitting error is 17.3cm, average error 11.5cm, and standard deviation 9.5cm. Instead, comparison of Leica backpack and TLS surveys leads to an average error of 4.7cm and standard deviation 0.6cm (4.2 cm and 0.3 cm, respectively, by excluding the final part of the left wing)

Recent Advances in Indoor Localization Systems and Technologies

Despite the enormous technical progress seen in the past few years, the maturity of indoor localization technologies has not yet reached the level of GNSS solutions. The 23 selected papers in this book present the recent advances and new developments in indoor localization systems and technologies, propose novel or improved methods with increased performance, provide insight into various aspects of quality control, and also introduce some unorthodox positioning methods

Sensor Fused Indoor Positioning Using Dual Band WiFi Signal Measurements

A ubiquitous and accurate positioning system for mobile devices is of great importance both to business and research due to the large number of applications and services it enables. In most outdoor environments this problem was solved by the introduction of the Global Positioning System (GPS). In indoor or suburban areas however, the GPS signals are often too weak to enable a reliable position estimate. Instead, other techniques must be utilized to provide accurate positioning. One of these is trilateration based on WiFi signal strengths. This is an auspicious technology to use partly because of the large number of access points (APs) in our everyday environment, and partly due to the possibility of measuring signal strength with a normal smartphone. The technique is further enabled by the move to include transmitters at 2.4 as well as 5 GHz in modern APs, providing a better basis for accurate position estimations. Furthermore, the motion sensors present in today’s smartphones are accurate enough to provide a short-time estimate of the user’s movement with high accuracy. In this thesis, both of these technologies are used to develop an accurate method for indoor positioning, and the contributions can be summed up into two points. The first contribution is an investigation of the behavior of two WiFi frequencies, 2.4 and 5 GHz, where their time dependent noise is proven to be almost uncorrelated with each other. This is then exploited to develop aWiFi-only trilateration algorithm by the use of a particle filter (PF), where the only restriction is that the locations of the APs need to be known. The second contribution is adding an accelerometer and a gyroscope to the algorithm, to provide a more accurate estimation. A step counter is developed using the accelerometer, and the gyroscope detects changes in heading while the WiFi signal strengths give information about the position. This makes it possible to alongside the position also estimate both heading and step length, while still keeping the only restriction of knowing the AP locations. The resulting algorithm produces position estimates with a mean error less than two meters for a specific use case, and around three meters when a more lenient user behavior is allowed

Computer Vision without Vision : Methods and Applications of Radio and Audio Based SLAM

The central problem of this thesis is estimating receiver-sender node positions from measured receiver-sender distances or equivalent measurements. This problem arises in many applications such as microphone array calibration, radio antenna array calibration, mapping and positioning using ultra-wideband and mapping and positioning using round-trip-time measurements between mobile phones and Wi-Fi-units. Previous research has explored some of these problems, creating minimal solvers for instance, but these solutions lack real world implementation. Due to the nature of using different media, finding reliable receiver-sender distances is tough, with many of the measurements being erroneous or to a worse extent missing. Therefore in this thesis, we explore using minimal solvers to create robust solutions, that encompass small erroneous measurements and work around missing and grossly erroneous measurements.This thesis focuses mainly on Time-of-Arrival measurements using radio technologies such as Two-way-Ranging in Ultra-Wideband and a new IEEE standard 802.11mc found on many WiFi modules. The methods investigated, also related to Computer Vision problems such as Stucture-from-Motion. As part of this thesis, a range of new commercial radio technologies are characterised in terms of ranging in real world enviroments. In doing so, we have shown how these technologies can be used as a more accurate alternative to the Global Positioning System in indoor enviroments. Further to these solutions, more methods are proposed for large scale problems when multiple users will collect the data, commonly known as Big Data. For these cases, more data is not always better, so a method is proposed to try find the relevant data to calibrate large systems

Puolivalvottu WLAN-radiokarttojen oppiminen

In this thesis a manifold learning method is applied to the problem of WLAN positioning and automatic radio map creation. Due to the nature of WLAN signal strength measurements, a signal map created from raw measurements results in non-linear distance relations between measurement points. These signal strength vectors reside in a high-dimensioned coordinate system. With the help of the so called Isomap-algorithm the dimensionality of this map can be reduced, and thus more easily processed. By embedding position-labeled strategic key points, we can automatically adjust the mapping to match the surveyed environment. The environment is thus learned in a semi-supervised way; gathering training points and embedding them in a two-dimensional manifold gives us a rough mapping of the measured environment. After a calibration phase, where the labeled key points in the training data are used to associate coordinates in the manifold representation with geographical locations, we can perform positioning using the adjusted map. This can be achieved through a traditional supervised learning process, which in our case is a simple nearest neighbors matching of a sampled signal strength vector. We deployed this system in two locations in the Kumpula campus in Helsinki, Finland. Results indicate that positioning based on the learned radio map can achieve good accuracy, especially in hallways or other areas in the environment where the WLAN signal is constrained by obstacles such as walls.Työssä sovelletaan monisto-oppimismenetelmää WLAN-paikannuksen ja automaattisen radiokartan luonnin ongelmaan. WLAN-signaalivoimakkuuksien mittausten luonteen takia käsittelemättömät mittaukset aiheuttavat epälineaarisia suhteita radiokartan mittauspisteiden välille. Nämä signaalivoimakkuusvektorit sijaitsevat avaruudessa jolla on korkea ulottuvuus. Niin kutsutun Isomap-algoritmin avulla kartan ulottuvuuksia voidaan karsia, jolloin sitä on helpompi työstää. Upottamalla karttaan merkittyjä avainpisteitä, se voidaan automaattisesti säätää vastaamaan mitattua ympäristöä. Ympäristö siis opitaan puolivalvotusti; keräämällä harjoituspisteitä ja upottamalla ne kaksiulotteiseen monistoon saadaan karkea kartta ympäristöstä. Kalibrointivaiheen jälkeen, jossa merkittyjä avainpisteitä käytetään yhdistämään moniston koordinaatit maantieteellisiin kohteisiin, voidaan suorittaa paikannusta säädetyn kartan avulla. Tämä voidaan tehdä perinteisen valvotun oppimisen avulla, joka tässä tapauksessa on yksinkertainen lähimmän naapurin löytäminen mitatulle signaalivoimakkuusvektorille. Järjestelmää kokeiltiin kahdessa paikassa Kumpulan kampuksessa Helsingissä. Tulokset viittaavat siihen että opitun radiokartan avulla paikannus voi saavuttaa hyvän tarkkuuden, etenkin käytävissä ja muissa tiloissa jossa esteet kuten seinät rajoittavat WLAN-signaalia

Comunicações óticas de alto débito em espaço livre

Signal distribution through high capacity links is nowadays a requirement that is becoming more crucial than ever. Therefore, the introduction of fifth generation mobile networks lead to the need for high capacity fronthaul and backhaul. Fiber distributions are commonly available in developed countries, however there are some areas that do not sustain this type of resource, such as in areas with low residential user density. To overcome the idea that resources are allocated only in these areas, free space optics (FSO) present a suitable and lower cost solution and can be used in temporary events (e.g. when the fiber is disrupted). Free space optics is an optical type of communication that requires line of sight, where the atmosphere is the transmission medium. Due to changes in the atmospheric conditions, free space optics systems suffer from variable attenuation. In the scope of this work, the atmospheric interaction is the subject of study. To accomplish link optimization, several alternatives are studied, being based on channel prediction along side with probabilistic constellation shaping. A concave mirror together with a positioning system is also used to overcome structure sway and other sources of pointing error. In the lab, the estimation processes are used to produce 64-QAM connection with variable transmission rates between 400 Gbit/s and 500 Gbit/s and the gain from using adaptive modulation is evaluated. In the last stage, an automatic gimbal positioning system is also tested for several control algorithms.Atualmente, a distribuição de sinais por meio de canais de alta capacidade é um requisito cada vez mais crucial. Nesse sentido, a progressiva introdução de novas tecnologias de acesso móvel de quinta geração desempenha um papel fundamental, fomentando a necessidade de desenvolver novas técnicas de transmissão de alto débito para redes de fronthaul e/ou backhaul. As distribuições de fibra estão bem disseminadas entre os países desenvolvidos, no entanto, existem algumas áreas que não sustentam esse tipo de recurso, o que é comum em regiões de baixa densidade de clientes residenciais. Para combater a ideia de que os recursos são alocados apenas nas grandes áreas, a ótica de espaço livre apresenta uma solução adequada. Alternativamente, devido à facilidade e rapidez de instalação, as comunicações óticas de espaço livre podem ser utilizadas como alternativa à fibra em casos de destruição da mesma. A comunicação ótica em espaço livre é um tipo de comunicação direcional que requer linha de vista, sendo a atmosfera o meio de propagação. Devido às variações atmosféricas, as comunicações oticas de espaço livre sofrem atenuação variável. No decorrer deste trabalho, a interação atmosférica é objeto de estudo. Para realizar a otimização do canal de transmissão, várias alternativas são estudadas, baseando-se na previsão de canais em tempo real em conjunto com modulação probabilística da constelação. Um espelho côncavo equipado com sistema de posicionamento é também usado para superar as vibrações e outras fontes de erro posicional. No laboratório, os processos de estimativa são usados para adaptar uma conexão 64-QAM com taxas de transmissão entre 400 Gbit/s e 500 Gbit/s. O ganho do uso da modulação adaptativa é avaliado face a formatos de modulação fixos. No último estágio, o sistema de posicionadores é também testado, com o intuito de avaliar o seu impacto na estabilidade do canal.Mestrado em Engenharia Eletrónica e Telecomunicaçõe

Visible Light Communication (VLC)

Visible light communication (VLC) using light-emitting diodes (LEDs) or laser diodes (LDs) has been envisioned as one of the key enabling technologies for 6G and Internet of Things (IoT) systems, owing to its appealing advantages, including abundant and unregulated spectrum resources, no electromagnetic interference (EMI) radiation and high security. However, despite its many advantages, VLC faces several technical challenges, such as the limited bandwidth and severe nonlinearity of opto-electronic devices, link blockage and user mobility. Therefore, significant efforts are needed from the global VLC community to develop VLC technology further. This Special Issue, “Visible Light Communication (VLC)”, provides an opportunity for global researchers to share their new ideas and cutting-edge techniques to address the above-mentioned challenges. The 16 papers published in this Special Issue represent the fascinating progress of VLC in various contexts, including general indoor and underwater scenarios, and the emerging application of machine learning/artificial intelligence (ML/AI) techniques in VLC