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@@ -4,7 +4,7 @@
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%Obviously, GNSS are of no practical use in the context of indoor localisation.
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Determining a position indoors is a challenging task.
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Besides the complex architecture of many buildings, \commentByLukas{kein a?} a high accuracy needs to be achieved, especially for buildings with many small separated areas like shopping malls or office blocks.
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Besides the complex architecture of many buildings, high accuracy needs to be achieved, especially for buildings with many small separated areas like shopping malls or office blocks.
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In recent years, many different systems were presented to meet those requirements.
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Especially Wi-Fi positioning and pedestrian dead reckoning (PDR) are very popular solutions.
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Approaches based on PDR try to estimate the current position given the previous position and thus require an initial state.
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@@ -14,21 +14,18 @@ Additional improvements can be achieved by using environmental information about
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In most cases, probabilistic methods are used to incorporate those highly different sensor types.
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Here, a probability distribution describes the pedestrian's possible whereabouts and therefore the uncertainty of the system.
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Drawing \commentByLukas{Drawing samples oder sampling} from a probability distribution and
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\commentByLukas{Willst du hier das Samplen erwaehnen? Es kommt so ein bisschen aus dem Nichts und man kann es gerade nur schwer einordnen} finding an analytical solution for densities is in most cases a difficult task, especially in case of time sequential, non-linear and non-Gaussian models.
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Drawing
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\commentByLukas{Drawing samples oder sampling}
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from a probability distribution and
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\commentByLukas{Willst du hier das Samplen erwaehnen? Es kommt so ein bisschen aus dem Nichts und man kann es gerade nur schwer einordnen}
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\commentByToni{Ich möchte hier auf Monte Carlo ueberleiten. Warum macht man das ueberhaupt? Ich finde das umschreibt das ganz gut. alles andere kostet nur unfassbar viel platz wie ich finde.}
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finding an analytical solution for densities is in most cases a difficult task, especially in case of time sequential, non-linear and non-Gaussian models.
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Due to the high complexity of the human movement, we consider indoor localisation as such.
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A broad class to obtain numerical results instead are \commentByLukas{kein the} the Monte Carlo (MC) methods.
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Here, a set of weighted random samples is used to solve any problem having a probabilistic interpretation. \commentByLukas{.. is used to solve the estimation process? Man loest ja nicht jedes probabilistische Problem damit?}
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By applying the time sequential hidden Markov process of Bayes filtering, one of the most important MC techniques results: particle filtering.
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A particle filter updates the state estimation recursively in time with every new incoming measurement using the state transition and state evaluation step. \commentByLukas{Das macht ja ganz allgemein der Bayes Filter und ist nicht nur spezifisch fuer Partikel filter}
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\commentByLukas{Vielleicht ein wenig umschreiben?:
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Bayesian filters solve such problems by updating the state estimation recursively with every new incoming measurement.
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A broad class to obtain numerical results for this approach are Monte Carlo (MC) methods, where a set of random samples is used to approximate the underlying probability distribution.
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By applying the time sequential hidden Markov process of Bayes filtering, one of the most important MC techniques results: particle filtering.
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Here, a set of weighted random samples is used to solve the state estimation process.}
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Here, a set of weighted random samples is used to solve the state estimation process.
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Based on this general methodology, many different approaches for estimating a position in indoor environments have been developed.
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All these approaches differ mainly in how the dynamics are modelled in the transition step and how a specific sensor measurement can be used for evaluation.
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@@ -37,8 +34,7 @@ The evaluation model is mostly separated into any number of sensor models, each
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For example, a barometer can be used to determine the probability of being on a certain floor \cite{Binghao13-UBI}.
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%Another example that demonstrates the big differences between single approaches is the large number of sensor models using Wi-Fi signal strengths. There are fingerprinting methods, which require an extensive offline calibration phase, signal strength prediction models like the log-distance model or wall-attenuation-factor model and many others \cite{Ville09, Fang09, Ebner:Thesis:2013}.
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Despite the many advances made in the last years, nearly all systems suffer from more or less the same problems \commentByLukas{Wuerde jetzt eine Aufzaehlung der Probleme der einzelnen Systeme erwarten. Stattdessen geht es direkt weiter mit Problemen von Sensormodellen. Den naechsten Satz vielleicht einfach weglassen, dann sollte es ok sein.}.
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Of course, every sensor model brings its very own weaknesses.
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Despite the many advances made in the last years, nearly all systems suffer from more or less the same problems.
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Like mentioned before, PDR suffers from an accumulating bias,
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the signal of Wi-Fi gets attenuated by walls
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\commentByFrank{falls noch platz ist: noch mehr nachteile :P \docWIFI{} location estimation strongly depends on the quality of the signal-strength estimation model (oder fingerprinting) and the way the smartphone is held}
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@@ -49,11 +45,10 @@ That is the reason for the use of statistical methods in the first place. Nevert
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Current transition models, which aim to approximate the movement, are still very restrictive and unable to handle unforeseen events.
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Faulty sensor measurements, like a falsely detected turn, can cause the estimation to lose track.
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For example by taking \commentByFrank{by taking -> by recognising?} a turn too soon and walking into a room instead of another big hallway.
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For example by recognising a turn too soon and walking into a room instead of another big hallway.
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Due to this, the filter needs some time to recover, which again takes a while because of the restrictive model (e.g. no walking through walls and only realistic walking speed).
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This temporal delay worsens the estimate immensely.
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A solution to recover from such filter divergences faster, is using
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\commentByFrank{is using -> involves?} methods to re-initialize the filtering procedure \cite{Nurminen2014}.
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A solution to recover from such filter divergences faster, involves methods to re-initialize the filtering procedure \cite{Nurminen2014}.
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However, even this can not completely prevent delays.
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Another reason for possible time delays are slow sensor updates.
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For example, most mobile devices restrict the Wi-Fi module to update only every few seconds, to save on battery.
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@@ -64,9 +59,7 @@ For example, most mobile devices restrict the Wi-Fi module to update only every
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\input{gfx/multimodalpath.eps_tex}
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\caption[An example of the occurrence of a multimodal distribution.]{
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An example of the occurrence of a multimodal distribution.
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At time $t-1$ the floor is separated by a wall and the mode of the distribution (coloured circle),
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\commentByFrank{mode of the weglassen? einfach: distribution ... splits}
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representing the current position, splits apart.
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At time $t-1$ the floor is separated by a wall and the distribution (coloured circle), splits apart.
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The most likely position (green line) is estimated somewhere in-between. After a right turn, the distribution slowly starts to recover its unimodality.}
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\label{fig:multimodalPath}
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\end{figure}
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@@ -90,13 +83,16 @@ Namely, forward-backward smoothing \cite{doucet2000} and backward simulation \ci
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Within this work, we investigate the benefits and drawbacks of those techniques using our indoor localisation system presented in \cite{Ebner-16}.
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We provide both, fixed-lag and fixed-interval smoothing as well as a novel approach for incorporating them easily within the localisation procedure.
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Additionally, we enrich the state transition model with an activity recognition to distinguish between walking, standing and walking stairs.
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The main goal is to solve above mentioned problems and to investigate new possibilities for even more advanced systems.
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All of our contributions are supported by an extensive experimental evaluation.
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\commentByLukas{In der Einleitung sollte an einer Stelle ganz klar die Contributions der Arbeit herausgestellt werden. Vielleicht irgendwie sowas: }
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\commentByLukas{In der Einleitung sollte an einer Stelle ganz klar die Contributions der Arbeit herausgestellt werden. Vielleicht irgendwie sowas:
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The contributions of this work are as follows:
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Firstly, we extend current smoothing methods for indoor localisation to resolve multimodalities during the state estimation process. Secondly, we incorporate the knowledge of the user's destination as a-priori knowledge. Thirdly, we enrich the state transition model with an activity recognition to distinguish between walking, standing and walking stairs. All of our contributions are supported by an extensive experimental evaluation.
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Firstly, we extend current smoothing methods for indoor localisation to resolve multimodalities during the state estimation process. Secondly, we incorporate the knowledge of the user's destination as a-priori knowledge. Thirdly, we enrich the state transition model with an activity recognition to distinguish between walking, standing and walking stairs. All of our contributions are supported by an extensive experimental evaluation. }
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\commentByToni{Steht doch direkt einen Absatz drueber nur halt kein plakatives "The contributions of " steht. Nur das Smoothing ist die Contribution meiner Meinung nach. Das prior knowledge ist ausm fusion paper. lediglich die activity rec fehlte. habe es ergänzt :). da bin ich mir aber noch nicht sicher... es wird ja nicht wirklich evaluiert sondern eher als "gegeben" angesehen. vielleicht dann auch eher so beschreiben?}
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