<p>This licentiate thesis argues that a key to understanding the embodiment of cognition is the “sharing” of neural mechanisms between sensorimotor processes and higher-level cognitive processes as described by simulation theories. Simulation theories explain higher-level cognition as (partial) simulations or emulations of sensorimotor processes through the re-activation of neural circuitry also active in bodily perception, action, and emotion. This thesis develops the notion that simulation mechanisms have a particular representational function, as off-line representations, which contributes to the representation debate in embodied cognitive science. Based on empirical evidence from neuroscience, psychology and other disciplines as well as a review of existing simulation theories, the thesis describes three main mechanisms of simulation theories: re-activation, binding, and prediction. The possibility of using situated and embodied artificial agents to further understand and validate simulation as a mechanism of (higher-level) cognition is addressed through analysis and comparison of existing models. The thesis also presents some directions for further research on modeling simulation as well as the notion of embodied simulation as off-line representation.</p> / Report code: LiU-Tek-Lic-2007:21.

<p>The Transmission Control Protocol (TCP) has been the dominant transport protocol in the Internet for many years. One of the reasons to this is that TCP employs congestion control mechanisms which prevent the Internet from being overloaded. Although TCP's congestion control has evolved during almost twenty years, the area is still an active research area since the environments where TCP are employed keep on changing. One of the congestion control mechanisms that TCP uses is fast retransmit, which allows for fast retransmission of data that has been lost in the network. Although this mechanism provides the most effective way of retransmitting lost data, it can not always be employed by TCP due to restrictions in the TCP specification.</p><p>The primary goal of this work was to investigate when fast retransmit inhibitions occur, and how much they affect the performance of a TCP flow. In order to achieve this goal a large series of practical experiments were conducted on a real TCP implementation.</p><p>The result showed that fast retransmit inhibitions existed, in the end of TCP flows, and that the increase in total transmission time could be as much as 301% when a loss were introduced at a fast retransmit inhibited position in the flow. Even though this increase was large for all of the experiments, ranging from 16-301%, the average performance loss, due to an arbitrary placed loss, was not that severe. Because fast retransmit was inhibited in fewer positions of a TCP flow than it was employed, the average increase of the transmission time due to these inhibitions was relatively small, ranging from 0,3-20,4%.</p>

<p>This thesis presents research on transport layer behavior in wireless networks. As the Internet is expanding its reach to include mobile devices, it has become apparent that some of the original design assumptions for the dominant transport protocol, TCP, are approaching their limits. A key feature of TCP is the congestion control algorithm, constructed with the assumption that packet loss is normally very low, and that packet loss therefore is a sign of network congestion. This holds true for wired networks, but for mobile wireless networks non-congestion related packet loss may appear. The varying signal power inherent with mobility and handover between base-stations are two example causes of such packet loss. This thesis provides an overview of the challenges for TCP in wireless networks together with a compilation of a number of suggested TCP optimizations for these environments. A TCP modification called TCP-L is proposed. It allows an application to increase its performance, in environments where residual bit errors normally give a degraded throughput, by making a reliability tradeoff. The performance of TCP-L is experimentally evaluated with an implementation in the Linux kernel. The transport layer performance in a 4G scenario is also experimentally investigated, focusing on the impact of the link layer design and its parameterization. Further, for emulation-based protocol evaluations, controlled packet loss and bit error generation is shown to be an important aspect.</p>

<p>Due to the cheap and flexible framework that the underlying IP-technology of the internet provides, IP-networks are becoming popular in more and more contexts. For instance, telecommunication operators have started to replace the fixed legacy telephony networks with IP-networks. To support a smooth transition towards IP-networks, the Stream Control Transmission Protocol (SCTP) was standardized. SCTP is used to carry telephony signaling traffic, and solves a number of problems that would have followed from using the Transmission Control Protocol (TCP) in this context. However, the design of SCTP is still heavily influenced by TCP. In fact, many protocol mechansisms in SCTP are directly inherited from TCP. Unfortunately, many of these mechanisms are not adapted to the kind of traffic that SCTP is intended to transport: time critical message-based traffic, e.g. telephony signaling.In this thesis we examine, and adapt some of SCTP's mechanisms to more efficiently transport time critical message-based traffic. More specifically, we adapt SCTP's loss recovery and message bundling for timely message transfers. First, we propose and experimentally evaluate two loss recovery mechanisms: a packet-based Early Retransmit algorithm, and a modified retransmission timeout management algorithm. We show that these enhancements can reduce loss recovery times with at least 30-50%, in some scenarios. In addition, we adapt the message bundling of SCTP to better support timely message delivery. The proposed bundling algorithm can in some situations reduce the transfer time of a message with up to 70%.In addition to these proposals we have also indentified and reported mistakes in some of the most popular SCTP implementations. Furthermore, we have continously developed the network emulation software KauNet to support our experimental evaluations.</p>

This thesis describes the VHDL behavioral model design of a DSP On Chip Emulation Unit. The prototype of this design is the OnCE port of the Motorola DSP56002. Capabilities of this On Chip Emulation Unit are accessible through four pins, which allows the user to step through a program, to set the breakpoint that stop program execution at a specific address, and to examine the contents of registers, memory, and pipeline information. The detailed design that includes input/output signals and sub blocks is presented in this thesis. The user will interact with the DSP through a GUI on the host computer via the RS232 port. An interface between the RS232 and On Chip Emulation Unit is therefore designed as well. The functionality is designed to be same as described by Motorola and it is verified by a test bench. The writing of the test bench, test sequence and results is presented also.

<p>This dissertation discusses the view that embodied cognition is essentially internal simulation (or emulation) of perception and action, and that the same (neural) mechanisms are underlying both real and simulated perception and action. More specifically, it surveys evidence supporting the simulation view from different areas of cognitive science (neuroscience, perception, psychology, social cognition, theory of mind). This is integrated with related research in situated robotics and directions for future work on internal simulation of perception and action in robots are outlined. In sum, the ideas discussed here provide an alternative view of representation, which is opposed to the traditional correspondence notions of representation that presuppose objectivism and functionalism. Moreover, this view is suggested as a viable route for situated robotics, which due to its rejection of traditional notions of representation so far has mostly dealt with more or less reactive behavior, to scale up to a cognitive robotics, and thus to further contribute to cognitive science and the understanding of higher-level cognition</p>

Η βελτιστοποίηση των συστημάτων επικοινωνίας πολλαπλών εισόδων-εξόδων (MIMO) απαιτεί τη δοκιμή τους υπό ρεαλιστικές συνθήκες και σε πολλά διαφορετικά περιβάλλοντα. Η δοκιμή απ’ ευθείας σε πραγματικά ασύρματα περιβάλλοντα δεν είναι αποδοτική μέθοδος, ειδικά κατά τα στάδια της σχεδίασης και του ελέγχου σωστής λειτουργίας, καθώς το κανάλι είναι πολύ ευαίσθητο, μη ελέγξιμο και μη αιτιατό. Επιπροσθέτως, η δοκιμή σε πραγματικά κανάλια δεν είναι πρακτική μέθοδος όταν χρειάζεται να δοκιμάσουμε πολλά διαφορετικά περιβάλλοντα ή να συμπεριληφθεί η κίνηση μέσα στις δοκιμές. Η δημιουργία ρεαλιστικών μοντέλων για κανάλια, χρησιμοποιώντας εργαλεία λογισμικού (Software) είναι μια δεύτερη επιλογή η οποία όμως δεν παράγει αποτελέσματα σε πραγματικό χρόνο και είναι επιπρόσθετα αρκετά χρονοβόρα. Ο λόγος είναι ότι αφού παραχθούν οι συντελεστές του καναλιού στο λογισμικό, η συνέλιξη των συντελεστών αυτών που συνιστούν την κρουστική απόκριση του καναλιού με τα μεταδιδόμενα σήματα είναι μια σχετικά αργή διαδικασία που θέτει φραγμούς στην εξομοίωση πραγματικού χρόνου. Σε κάποια συστήματα δοκιμών βασισμένα σε λογισμικό, τα διαμορφωμένα δεδομένα και τα διαλείπτοντα σήματα συντίθεται ώστε να δημιουργήσουν μιγαδικές (I/Q) κυματομορφές οι οποίες μεταφορτώνονται στη μνήμη μιας γεννήτριας αυθαίρετων κυματομορφών για να παραχθούν από τη γεννήτρια ραδιοκυμάτων. Υπάρχουν αρκετά εργαλεία λογισμικού που μπορούν να επιταχύνουν τη διαδικασία δημιουργίας κυματομορφών με διαλείψεις, όπως για παράδειγμα το εργαλείο MatlabΤΜ της εταιρείας MathWorks, αλλά αυτά περιορίζονται στα παραδοσιακά μοντέλα διαλείψεων. Ακόμα οι γεννήτριες αυθαίρετων κυματομορφών διαθέτουν περιορισμένη μνήμη, με αποτέλεσμα οι παραγόμενες κυματομορφές να είναι αρκετά μικρές και να επαναλαμβάνονται απλώς στο χρόνο. Για όλους αυτούς τους λόγους χρειάζεται να επιστρατεύσουμε ειδικού σκοπού υλικό το οποίο εξομοιώνει ρεαλιστικά κανάλια πολλαπλών εισόδων-εξόδων ώστε να δώσουμε μια λύση στις απαιτητικές αυτές συνθήκες εξομοίωσης. Στην παρούσα διπλωματική σχεδιάσαμε έναν προσομοιωτή καναλιών για κανάλια βασικής ζώνης πολλαπλών εισόδων πολλαπλών εξόδων (baseband MIMO), σε αρχιτεκτονική υλικού και συγκεκριμένα σε συστοιχίες προγραμματιζόμενων πυλών (FPGA). Ο προσομοιωτής αυτός μπορεί να χρησιμοποιηθεί για την πιστοποίηση της λειτουργίας μιας σειράς επεξεργαστών για σύγχρονα και επόμενης γενιάς τηλεπικοινωνιακά συστήματα. / Optimization of multiple input multiple output (MIMO) communication systems, requires testing under realistic conditions and various channel environments. Direct tests on real-world channel environments, is not an efficient method since the channel is very sensitive, not controllable and non–causal. Moreover, testing in a real channel is not a practical method when various different channels need to be tested or mobility to be included in the tests. A second option is to create realistic channel models, using software tools but this does not produce real time results and can also be prohibitively time-consuming. The reason for this, is that after creating the channel coefficients in software that form the channel’s impulse response, the convolution of these coefficients with the transmitted signals is a relatively slow process that hinders real-time simulation. In some software-based test systems the modulated data and fading signals are used to create complex (I/Q) waveforms that are downloaded into the memory of an arbitrary waveform generator in order to be generated by the RF signal generator. Many software tools exist, that can accelerate the process of fading waveform creation, such as MathWorks’ MatlabΤΜ but these tools are limited to traditional fading models. Moreover the arbitrary waveform generators consist of limited memory resulting in short waveforms that simply repeat over time. For these reasons, a requirement for specialized instrumentation arises, one that can emulate realistic multiple input-multiple output channels, in order to provide an efficient solution to these demanding simulation conditions. In the context of the current thesis, we design a baseband multiple input-multiple output (MIMO) emulator into hardware, specifically into Field Programmable Gate Array (FPGA). This particular hardware component is suitable for the functional verification of a variety of baseband processors for current and next generation telecom equipment.

Η συμπεριφορά των NAND Flash μνημών, της πιο επιτυχημένης τε- χνολογίας Non-Volatile μνημών σήμερα, αλλοιώνεται με την αύξηση των εγγραφών. Αυτή η διαδικασία, που ονομάζεται γήρανση, πέρα από μη ανα- στρέψιμη είναι και πολύ σημαντική για τον σχεδιασμό συστημάτων που χρησιμοποιούν NAND Flash μνήμες (π.χ. SSD), επειδή επηρεάζει την ΙΟ απόδοση και την αξιοπιστία του συστήματος. Τα πειράματα πάνω σε πραγ- ματικές NAND Flash μνήμες είναι χρονοβόρες και μη αναστρέψιμες δια- δικασίες, καθώς νέες εγγραφές στην μνήμη αυξάνουν την γήρανση και η συμπεριφορά του συστήματος αλλάζει. Σκοπός της παρούσας διπλωματικής εργασίας, είναι η ανάπτυξη ενός συστήματος που θα μπορεί να εξομοιώσει σε πραγματικό χρόνο και με με- γάλη ακρίβεια την συμπεριφορά NAND Flash μνημών με συνθήκες γή- ρανσης παραμετροποιημένες από τον χρήστη. Τα βασικά πλεονεκτήματα αυτής της προσέγγισης είναι τα ακόλουθα: η τεχνολογία που εξομοιώνεται μπορεί να χρησιμοποιηθεί υπό ίδιες συνθήκες γήρανσης για επαναληπτικά πειράματα και το ίδιο σύστημα μπορεί να χρησιμοποιηθεί για να συγκρίνει διαφορετικές τεχνολογίες μνημών υπό διαφορετικές συνθήκες γήρανσης χρησιμοποιώντας τις ίδιες ρυθμίσεις hardware. / The behavior of NAND Flash, the most successful non-volatile memory technology today, deteriorates as the number of write accesses increases. This process, known as aging, is not only irreversible but also critical for the design of systemsthat use NAND Flash (ie. Solid-State Drives), since it affects the system’s IO performance and the required overhead for achieving a specific level of reliability. Experimental characterization of NAND Flash-based systems during their whole lifetime is a time-consuming and non-repetitive process, since further programming cycles increase aging, and the system's behavior changes. In this work, we present the architecture and experimental resultsof a system that can be used to emulate in real-time and with high precision the behavior of NAND Flash memories underuser-defined aging conditions. The main advantages of this approach are the following: the emulated technology can be used under the same aging conditions for repetitive experiments and under different aging conditions using the same hardware setup.

<p>Current frontiers in complex stochastic modeling of high-dimensional processes include major emphases on so-called functional data: problems in which the data are snapshots of curves and surfaces representing fundamentally important scientific quantities. This thesis explores new Bayesian methodologies for functional data analysis. </p><p>The first part of the thesis places emphasis on the role of factor models in functional data analysis. Data reduction becomes mandatory when dealing with such high-dimensional data, more so when data are available on a large number of individuals. In Chapter 2 we present a novel Bayesian framework which employs a latent factor construction to represent each variable by a low dimensional summary. Further, we explore the important issue of modeling and analyzing the relationship of functional data with other covariate and outcome variables simultaneously measured on the same subjects.</p><p>The second part of the thesis is concerned with the analysis of circadian data. The focus is on the identification of circadian genes that is, genes whose expression levels appear to be rhythmic through time with a period of approximately 24 hours. While addressing this goal, most of the current literature does not account for the potential dependence across genes. In Chapter 4, we propose a Bayesian approach which employs latent factors to accommodate dependence and verify patterns and relationships between genes, while representing the true gene expression trajectories in the Fourier domain allows for inference on period, phase, and amplitude of the signal.</p><p>The third part of the thesis is concerned with the statistical analysis of computer models (simulators). The heavy computational demand of these input-output maps calls for statistical techniques that quickly estimate the surface output at untried inputs given a few preliminary runs of the simulator at a set design points. In this regard, we propose a Bayesian methodology based on a non-stationary Gaussian process. Relying on a model-based assessment of uncertainty, we envision a sequential design technique which helps choosing input points where the simulator should be run to minimize the uncertainty in posterior surface estimation in an optimal way. The proposed non-stationary approach adapts well to output surfaces of unconstrained shape.</p> / Dissertation

This thesis presents a general simulation framework used for evaluating the performance of bilateral teleoperation systems under consistent and controllable network conditions. A teleoperation system is where an operator uses a master device to control a slave robot through a communication link. The communication link between the master and slave has an important impact on the system performance. Network emulation using ns-2 has been proposed as a way of simulating the communication link. It allows for the network conditions to be controlled and for repeatable results. The proposed setup was used to test the performance of a hydraulic actuator under various conditions of wired and wireless networks. Three control schemes were evaluated using various combinations of time delay and packet loss. The system was also tested simulating wireless communication between the master and slave to determine the effects of transmission power and distance on the performance of the system.