Reconstructing Popov v. Hayashi in a framework for argumentation with structured arguments and Dungean semantics Abstract In this article the argumentation structure of the court's decision in the Popov v. Hayashi case is formalised in Prakken's (Argument Comput 1:93-124; 2010) abstract framework for argument-based inference with structured arguments. In this framework, arguments are inference trees formed by applying two kinds of inference rules, strict and defeasible rules. Arguments can be attacked in three ways: attacking a premise, attacking a conclusion and attacking an inference. To resolve such conflicts, preferences may be used, which leads to three corresponding kinds of defeat, after which Dung's (Artif Intell 77:321-357; 1995) abstract acceptability semantics can be used to evaluate the arguments. In the present paper the abstract framework is instantiated with strict inference rules corresponding to first-order logic and with defeasible inference rules for defeasible modus ponens and various argument schemes. The main techniques used in the formal reconstruction of the case are rule-exception structures and arguments about rule validity. Arguments about socio-legal values and the use of precedent cases are reduced to arguments about rule validity. The tree structure of arguments, with explicit subargument relations between arguments, is used to capture the dependency relations between the elements of the court's decision. This article presents a formalisation of the Popov v. Hayashi case in an instance of Prakken's (2010) framework for argument-based inference with structured arguments. This framework further develops Amgoud et al. (2006) 's attempt to integrate work on rule-based argumentation of Pollock (1994) , Vreeswijk (1997) , Prakken and Sartor (1997) and others. It defines arguments as inference trees formed by applying two kinds of inference rules, strict and defeasible rules. This naturally leads to three ways of attacking an argument: attacking a premise, attacking a conclusion and attacking an inference. To resolve such conflicts, preferences may be used, which leads to three corresponding kinds of defeat: undermining, rebutting and undercutting defeat. The framework is abstract in that it applies to any set of inference rules, as long as it is divided into strict and defeasible ones, and to any logical language with a contrary relation defined over it. Moreover, since it associates each knowledge base with a set of arguments ordered by a binary relation of defeat, the acceptability status of arguments can be defined in terms of Dung's (1995) well-understood abstract approach to argument acceptability.. The choice for tree-structured arguments based on two types of inference rules arguably is very natural, not only in light of logic and argumentation theory but also when looking at argumentation as it occurs in human thinking and dialogue. The notion of arguments as trees of inferences is very common in standard logic and in argumentation theory, and it is the basis of many software tools for argument visualisation. Moreover, in actual argumentation humans often express their arguments as claims supported with one or more premises, which can in turn be supported with further premises, and so on, which results in tree structures. The tree form is therefore very suitable for capturing the dependency relations between the various elements of the court's decision. Finally, the framework is very suited for modelling reasoning with argumentation schemes, by regarding such schemes as defeasible inference rules.. The instance of the framework assumed in this paper will draw on my previous work (partly with others) on rule-based argumentation (Prakken and Sartor 1997) , reasoning with argument schemes (Bex et al. 2003; Prakken 2005a) , accrual of arguments (Prakken 2005b) and reasoning under burden of proof (Prakken and Sartor 2009 ).. The main purpose of the present reconstruction is theoretical, namely, to test the adequacy of the framework of Prakken (2010) for giving a formal reconstruction of the Popov v. Hayashi case. More precisely, the object of the formalisation is the relevant facts and rules stated by judge McCarthy and the arguments constructed by him on the basis of these facts and rules. The reconstruction will not be descriptive but rational: the aim is to reconstruct the judge's reasoning as being, as far as possible, rationally sound. Assuming that the judge's reasoning in the case is by and large sound, the extent to which such a reconstruction is possible indicates the suitability of the formal framework.. A secondary aim of the case study is more practical, namely, to give a reconstruction as could be made by lawyers or law students with so-called sensemaking software. With such software, e.g. Reed and Rowe's (2004) Araucaria or Van den Braak's (2010) Avers, users can draft their own arguments or analyse given arguments, in order to improve the quality of their arguments or to better grasp the issues in a case. The present case study is also meant to test the suitability of the framework of Prakken (2010) as a theoretical basis for the design of sensemaking software for legal applications. Since users of such software will not be experts in knowledge representation, the main focus of this case study is on the general structure of arguments and their relations instead of on detailed knowledge representation issues, such as time, action, causation and intention. The only representation issues that will be discussed in detail are the representation of the validity of rules and of rule-exception structures, since these issues turn out to be crucial for capturing judge McCarthy's reasoning. The focus on sensemaking applications also means that the reconstruction of the case is ideally as close to the judge's actual formulation as possible, within the bounds defined by the primary aim to give a rational instead of purely descriptive reconstruction of the case.. This article is organised as follows. First in Sect. 2 the instance of Prakken's (2010) framework used in this article will be semi-formally presented. Then in Sect. 3 the formalisation of the case will be described in two parts: the facts (Sect. 3.1) and the legal analysis (Sect. 3.2). This section only presents the facts and rules discussed by judge McCarthy; the arguments that he constructs from them are presented in Sect. 4. The formalisation will be evaluated in Sect. 5. The aim of this paper was to test the suitability of the abstract framework of Prakken (2010) for modelling the argumentation structure of judge McCarthey's decision. Although a definite conclusion can only be drawn after comparing the present reconstruction with the other ones submitted to this issue, it can be tentatively concluded that the formalism is suitable. The abstract rule-based nature of the formalism turned out to be suitable for modelling the argument schemes used in the case, while the tree-structure of the arguments captured the dependencies between the elements in the judge's decision. Also, the three classes of conflict between arguments were sufficient to capture all conflicts in the case and Dung's (1995) acceptability semantics sufficed for capturing the outcome of the case, including a proper handling of the burden of proof. The two main technical devices that were needed were rule-exception structures and arguments about the validity of rules. The latter proved sufficient to capture value-based reasoning, since the only value that was at stake in this case, fairness, was reconstructed as a condition of a validity rule. For this reason more sophisticated models of value-based reasoning, such as those of Prakken (2002) or Bench-Capon (2003) , in which values are used to resolve conflicts between arguments, were not needed. Arguments about validity also proved useful in modelling the use of cases, since cases were by McCarthy mostly used as sources of rules (see also Verheij 2008) . There was no need to use more sophisticated models of legal case-based reasoning such as those discussed by Ashley (2006) but there was a need for an argument scheme for analogical rule application. Finally, the present reconstruction contains some examples of argument accruals but they were not relevant for the outcome of the case.. It is interesting to compare the present reconstruction with the only reconstruction available in the literature, the one of Wyner et al. (2007) . Being a conference paper, their reconstruction is less detailed than the present one. Wyner et al. also make use of domain-specific defeasible rules and argument schemes; like the present paper they use defeasible modus ponens and schemes for witness testimony and video tape, while in addition they use a 'scheme from purpose' to model the teleological aspects of the case. The legal analysis is mostly reconstructed with ruleexception structures; no rule validity rules are used. One main difference with the present reconstruction is in the treatment of socio-legal values. While in the present reconstruction the inclusion of the fairness condition in the validity rule v 4 made McCarthy's considerations on fairness a matter of rule validity, in Wyner et al.'s reconstruction values are used to resolve conflicts between arguments (based on Bench-Capon 2003) . In my opinion, the present account is closer to the actual wording of McCarthy's decision. In fact, besides fairness Wyner et al. include a second value of public order in their analysis. In the present reconstruction this value was not included since it cannot easily be based on statements of McCarthy.. A second main difference is that Wyner et al. use a different conception of arguments, in which each applicable rule gives rise to a separate argument in an abstract argumentation framework in the sense of Dung (1995) and in which there are no subargument relations between arguments. Instead, an argument applying a rule 'if q then p' can be attacked by an argument 'not p?', which can then be counterattacked with an argument applying a rule 'if r then q'. Applying any of Dung's (1995) then yields that the argument for p is reinstated by the argument for q, so that the arguments for p and q are justified and the argument 'not q?' is overruled. In the present approach instead a two-steps argument is created with premise r, intermediate conclusion q and final conclusion p, and no counterargument is needed. In my opinion, this better captures the dependency relations between the elements of arguments, since complex arguments are usually not expressed with the attack-counterattack relations of 2007's method. It seems better to regard 'not q'? not as stating a counterargument but as a separate kind of speech act, namely a challenge 'why q?' of the premises of an argument, which can be replied to with a further argument for that premise. Such speech acts can be modelled by embedding an argumentation logic in a dialogue system for argumentation, as in e.g. Gordon (1994); Prakken (2005c) . For a case study that applies this idea see Prakken (2008) .. An important question is to what extent the results of the present case study can be generalised. Strictly speaking this requires an experiment with a substantial number of cases but this goes beyond the scope of the present issue. A comparison can be made, however, with Prakken (2008) , in which a similar formalism was applied to a reconstruction of a Dutch civil ownerships dispute. In that case study not just the final decision was reconstructed but also the preceding stages of the proceeding, for which reason in Prakken (2008) I had to embed a model of argument-based inference in a dialogue model of legal argument. As for the inferential part, the earlier case study also used rule-exception structures and the argument scheme from witness testimony, while in addition it used priority arguments; on the other hand, no validity arguments or arguments about values were used. The case contained an explicit shift in the burden of persuasion, which required the use of Prakken's (2001) adapted definition of justification of arguments.. As I observed earlier in Prakken (2008) , case files often leave a considerable part of the relevant law implicit, since the law is assumed known to all parties. In Prakken (2008) this was not a serious problem, since the case was from a jurisdiction with which I am familiar. However, in the present case this is different. In experiments like the present one, where researchers are invited to perform case studies in jurisdictions with which they may not be familiar, this is an inevitable methodological problem. Nevertheless, when interpreted with care, case studies are a necessary complement to designs of formalisms or architectures, to reduce the risk that these designs are based on too simple accounts of legal reasoning.. Open Access This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.

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ON TRANSITION MINIMALITY OF BIDETERMINISTIC AUTOMATA Bideterministic automata are deterministic automata with the property of their reversal automata also being deterministic. Bideterministic automata have previously been shown to be unique (up to an isomorphism) minimal NFAs with respect to the number of states. In this paper, we show that in addition to state minimality, bideterministic automata are also transition-minimal NFAs. However, as this transition minimality is not necessarily unique, we also present the necessary and sufficient conditions for a bideterministic automaton to be uniquely transition-minimal among NFAs. These results are obtained using the notion of the universal automaton. We also present some properties of the universal automaton. Furthermore, we show that bideterministic automata are transition-minimal ∊-NFAs.

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Quantum Lower Bound for Recursive Fourier Sampling One of the earliest quantum algorithms was discovered by Bernstein and Vazirani, for a problem called Recursive Fourier Sampling. This paper shows that the Bernstein-Vazirani algorithm is not far from optimal. The moral is that the need to "uncompute" garbage can impose a fundamental limit on efficient quantum computation. The proof introduces a new parameter of Boolean functions called the "nonparity coefficient," which might be of independent interest.Like a classical algorithm, a quantum algorithm can solve problems recursively by calling itself as a subroutine. When this is done, though, the algorithm typically needs to call itself twice for each subproblem to be solved. The second call's purpose is to uncompute 'garbage' left over by the first call, and thereby enable interference between different branches of the computation. Of course, a factor of 2 increase in running time hardly seems like a big deal, when set against the speedups promised by quantum computing. The problem is that these factors of 2 multiply, with each level of recursion producing an additional factor. Thus, one might wonder whether the uncomputing step is really necessary, or whether a cleverly designed algorithm might avoid it. This paper gives the first nontrivial example in which recursive uncomputation is provably necessary.The example concerns a long-neglected problem called Recursive Fourier Sampling (henceforth RFS), which was introduced by Bernstein and Vazirani [5] in 1993 to prove the first oracle separation between BPP and BQP. Many surveys on quantum computing pass directly from the Deutsch-Jozsa algorithm [8] to the dramatic results of Simon [14] and Shor [13] , without even mentioning RFS. There are two likely reasons for this neglect. First, the RFS problem seems artificial. It was introduced for the sole purpose of proving an oracle result, and is unlike all other problems for which a quantum speedup is known. (I will define RFS in Section 1; but for now, it involves a tree of depth log n, where each vertex is labeled with a function to be evaluated via a Fourier transform.) Second, the speedup for RFS is only quasipolynomial (n versus n log n ), rather than exponential as for the period-finding and hidden subgroup problems.Nevertheless, I believe that RFS merits renewed attention-for it serves as an important link between quantum computing and the ideas of classical complexity theory. One reason is that, although other problems in BQP-such as the factoring, discrete logarithm, and 'shifted Legendre symbol ' problems [16]-are thought to be classically intractable, these problems are quite low-level by complexity-theoretic standards. They, or their associated decision problems, are in NP ∩ coNP.1 By contrast, Bernstein and Vazirani [5] showed that, as an oracle problem, RFS lies outside NP and even MA (the latter result is unpublished, though not difficult). Subsequently Watrous [17] gave an oracle A, based on an unrelated problem, for whichGreen and Pruim [10] gave an oracle B for which BQP B ⊂ P NP B . However, Watrous' problem was shown by Babai [3] to be in AM, while Green and Pruim's problem is in BPP. Thus, neither problem can be used to place BQP outside higher levels of the polynomial hierarchy PH.On the other hand, Umesh Vazirani and others have conjectured that RFS is not in PH, from which it would follow that there exists an oracle A relative to which BQP A ⊂ PH A . Proving this is, in my view, one of the central open problems in quantum complexity theory. Its solution seems likely to require novel techniques for constant-depth circuit lower bounds. 2 Actually, to place BQP outside MA relative to an oracle, it suffices to consider the complement of Simon's problem ("Does f (x) = f (x ⊕ s) only when s = 0?").3 For the RFS function can be represented by a low-degree real polynomial-this follows from the existence of a polynomial-time quantum algorithm for RFS, together with the result of Beals et al. [4] relating quantum algorithms to low-degree polynomials.

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Finitely additive extensions of distribution functions and moment sequences: The coherent lower prevision approach ABSTRACT. We study the information that a distribution function provides about the finitely additive probability measure inducing it. We show that in general there is an infinite number of finitely additive probabilities associated with the same distribution function. Secondly, we investigate the relationship between a distribution function and its given sequence of moments. We provide formulae for the sets of distribution functions, and finitely additive probabilities, associated with some moment sequence, and determine under which conditions the moments determine the distribution function uniquely. We show that all these problems can be addressed efficiently using the theory of coherent lower previsions. This paper consists of two parts, each devoted to one of two specific, but related, problems.. The first problem is: To what extent does a distribution function determine a probability measure? This question has a well-known answer when we are talking about probability measures that are σ -additive. We believe the corresponding problem for probability measures that are only finitely additive has received much less attention. This paper tries to remedy that situation somewhat by studying the particular case of finitely additive probability measures on the real unit interval [0, 1] (or equivalently, after an appropriate transformation, on any compact real interval). For this study, it will be very convenient to use the mathematical machinery behind Walley's [27] theory of coherent lower previsions, for which we introduce the basics in Section 2.. We shall see that, generally speaking, there is an infinite (closed and convex) set M (F) of finitely additive probability measures that correspond to a given distribution function F. However, by their very nature, and contrary to the sigma-additive case, finitely additive probabilities on an infinite set that extend 'something' are usually inconstructibles, meaning that they cannot actually be constructed, but that their existence may be inferred from the Hahn-Banach Theorem (or even stronger, the Axiom of Choice); see [25, Sections 12 .31 and 6.6] for more details. It was one of Walley's achievements to show that we can efficiently and constructively deal with them not by looking at the members of M (F) individually, but by working with their lower envelope E F , which in his language is called the natural extension of the distribution function F.. 1 Not only can this lower envelope always be constructed explicitly, but it is the closest we can get in a constructive manner to the finitely additive probabilities themselves. It turns out to be a coherent lower prevision with very special properties.. The set of finitely additive probabilities with a given distribution function has been considered before by Bruno de Finetti [13, Chapter 6] , who seems to suggest 2 that the value E F ( f ) of this natural extension in a function f is actually given by the lower RiemannStieltjes integral (RS) 1 0 f (x) dF(x) of f with respect to the distribution function F. We study the relationship between E F and lower Riemann-Stieltjes integrals in Section 3, and we shall see in Theorem 1 that de Finetti's suggestion needs some qualification, as it is essentially only correct when F is right-continuous.. In the second part, from Section 4 onwards, we address the second question: Is a distribution function uniquely determined by the corresponding sequence of moments? In a companion paper [21] , we have studied the set of finitely additive probabilities M (m) that produce a given moment sequence m. The fundamental step we take there is analogous to the one followed in the present paper for distribution functions. It consists of not considering the finitely additive probabilities in M (m) themselves, but to study their lower envelope E m , which is a coherent lower prevision with very special properties too. In answering the second question, we build on those results, but by looking at distribution functions we are also able to extend them.. We shall establish that a distribution function F uniquely determines its moment sequence m. In Section 4 then, we investigate to what extent, conversely, a moment sequence determines the distribution function. For distribution functions coming from σ -additive probability measures, the relation between moment sequences and distribution functions is well-known to be one-to-one, but again, the answer is not so clear when we let go of the assumption of σ -additivity. We shall prove that in general there may be an infinite number of distribution functions with the same moment sequence, and investigate under which conditions the distribution function is unique.. It will perhaps not come as too much of a surprise, at this point, that we can show that the set of finitely additive probability measures M (m) that corresponds to a moment sequence is the union of the sets M (F) over all the distribution functions F that are compatible with the moment sequence m. This is also done in Section 4 (see Theorem 6) . In Section 5, we further exploit the connection between distribution functions and moment sequences to come up with a number of quite interesting formulae expressing E m (i) as a convex mixture of a lower Riemann-Stieltjes integral and so-called lower oscillation functionals associated with point probability masses (see Theorem 14) ; and (ii) as a σ -additive convex mixture of completely monotone lower previsions associated with neighbourhood filters, which express that all probability mass is concentrated in arbitrarily small neighbourhoods of elements of the unit interval (see Theorem 16) . In passing, we give an alternative, constructive proof of the F. Riesz Representation Theorem (see Theorem 8 and Remark 4).

O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Mobile relay configuration in data-intensive Wireless Sensor Networks Recently, Wireless Sensor Networks (WSNs) have become increasingly available for data-intensive applications such as micro-climate monitoring, precision agriculture, and audio/video surveillance. A key challenge faced by data-intensive WSNs is to transmit the sheer amount of data generated within an application's lifetime to the base station despite the fact that sensor nodes have limited power supplies such as batteries or small solar panels. In this paper, we propose to use low-cost disposable mobile relays to reduce the energy consumption of data-intensive WSNs. Different from previous work, our approach does not require complex motion planning of mobile nodes, and hence can be implemented on a number of low-cost mobile sensor platforms. Moreover, we integrate the energy consumption due to both mobility and wireless transmissions into a holistic optimization framework. The optimal relay configuration is shown to depend on both the positions of nodes and the amount of data to be sent. We develop two algorithms that iteratively refine the configuration of mobile relays and converge to the optimal solution. These algorithms have efficient distributed implementations that do not require explicit synchronization. Our simulation results based on realistic energy models obtained from existing mobile and static sensor platforms show that our algorithms significantly outperform the best existing solutions. Recent years have seen the deployments of WSNs in a variety of data-intensive applications including micro-climate and habitat monitoring [1] , precision agriculture, and audio/video surveillance [2] . It is shown in [3] that a moderate-size WSN can gather up to 1 Gb/year from a biological habitat. Due to the limited storage capacity of sensor nodes, most data must be transmitted to the base station for archiving and analysis. However, sensor nodes must operate on limited power supplies such as batteries or small solar panels. Therefore, a key challenge faced by dataintensive WSNs is to minimize the energy consumption of sensor nodes such that the sheer amount of data generated within the lifetime of the application can be transmitted to the base station.. Recent work showed that the energy cost of WSNs can be significantly reduced by utilizing the mobility of nodes. Several different approaches have been proposed. A robotic unit may move around the network and collect data from static nodes through one-hop or multi-hop transmissions [4] - [8] . The mobile node may serve as the base station or a "data mule" that transports data between static nodes and the base station [9] - [11] . Mobile nodes may also be used as relays [12] that forward the data from source nodes to the base station. Several movement strategies for mobile relays have been studied in [12] , [13] .. Although the effectiveness of mobility in energy conservation is demonstrated by previous studies, the following key issues have not been addressed collectively. First, the movement cost of mobile nodes is not accounted for in the total network energy consumption. Instead, mobile nodes are often assumed to have replenishable energy supplies. For instance, a mobile node may periodically recharge its battery at a fixed charging dock [7] . However, energy replenishment is not always feasible due to the constraints of the physical environment. Second, complex motion planning of mobile nodes is often assumed in existing solutions which introduces significant design complexity and manufacturing costs. In [7] , [8] , [14] , [15] , mobile nodes need to compute optimal motion paths and continuously change their orientation and/or speed of movement. Such capabilities are usually not supported by existing low-cost mobile sensor platforms. For instance, Robomote [16] nodes are designed using 8-bit CPUs and small batteries that only last for about 25 minutes in full motion. Complex motion planning is not practical for such platforms due to the limited computational power and short battery lifetime.. In this paper, we use low-cost disposable mobile relays to reduce the total energy consumption of dataintensive WSNs. Different from mobile base station or data mules, mobile relays do not transport data; instead, they move to different locations and then remain stationary to forward data along the paths from sources to the base station. As a result, the communication delays can be significantly reduced compared with using mobile stations or data mules.. Our approach is motivated by the current state of mobile sensor platform technology. On the one hand, numerous low-cost mobile sensor prototypes such as Packbot [14] , Robomote [16] , Khepera [17] , and FIRA [18] are now available. Their manufacturing cost is comparable to that of typical static sensor platforms. As a result, they can be massively deployed in a network and used in a disposable manner. Our approach takes advantage of this capability by assuming that we have a large number of mobile relay nodes. On the other hand, due to low manufacturing cost, existing mobile sensor platforms are typically powered by batteries and only capable of limited mobility. Consistent with this constraint, our approach only requires simple motions of mobile relays, Le., one-shot relocation to designated positions after deployment. Compared with our approach, existing mobility approaches (such as mobile base station and data mule) typically assume a small number of powerful mobile nodes, which does not exploit the availability of massive low-cost mobile nodes.. We make the following contributions in this paper. (1) We formulate the problem of Optimal Mobile Relay Configuration in data-intensive WSNs. Our objective of energy conservation is holistic in that the total energy consumed by both mobility of relays and wireless transmissions is minimized, which is in contrast to existing mobility approaches that only minimize the transmission energy consumption. The tradeoff in energy consumption between mobility and transmission is exploited by configuring the positions of mobile relays. (2) We develop two algorithms that iteratively refine the configuration of mobile relays and converge to the optimal solution. We show that the optimal position for a mobile relay is not the midpoint of its neighbors, which is in contrast to the result of several previous studies [13] , [19] that only account for transmission costs. Instead, the optimal relay configuration depends on both the initial positions of nodes and the amount of data to be transmitted. Our optimal 81 algorithms have efficient distributed implementations that do not require explicit synchronization. (3) We conduct extensive simulations based on realistic energy models obtained from existing mobile and static sensor platforms. Our results show that our algorithms can reduce energy consumption by roughly 23% compared to the best existing solutions.. The rest of the paper is organized as follows. Section 2 reviews related work. In Section 3, we formally define our problem. We propose an iterative algorithm for the single-flow problem in Section 4. In Section 5, we extend our solution to the multi-flow problem. Section 6 describes our simulation results and Section 7 concludes this paper. In this paper, we proposed a holistic approach to minimize the total energy consumed by both mobility of relays and wireless transmissions. Most previous work ignored the energy consumed by moving mobile relays. We developed an iterative approach to compute the optimal positions of relay nodes that can be implemented in a centralized or distributed fashion. Our algorithms are appropriate for a variety of dataintensive wireless sensor networks. In both single flow and multiple flow patterns, we show that our holistic approach can reduce total energy consumption by up to 23% compared to previous approaches. The optimal position for a mobile relay is not the midpoint of its neighbors; instead, it converges to this position as the amount of data transmitted goes to infinity. Our algorithms allow some nodes to move while others do not because any local improvement for a given mobile relay is a global improvement. This allows us to potentially extend our approach to handle additional constraints on individual nodes such as low energy levels or mobility restrictions due to application requirements .. Our algorithms are optimal when the transmission routes are predetermined and participating nodes remain the same throughout different configurations. In some cases, it may be beneficial to insert a new relay along the transmission path after several rounds if the new route moves into its proximity, or alternatively, drop a node if the route moves away from it. For future work, we plan on studying the problem of finding the optimal routes along with the optimal locations of ;; 3000 nodes on those routes. We review three different approaches, mobile base stations, data mules, and mobile relays, that use mobility to reduce energy consumption. A mobile base station moves around the network and collects data from the nodes. In some work, all nodes are always performing multiple hop transmissions to the base station, and the goal is to rotate which nodes are close to the base station in order to balance the transmission load [4] - [6] . In other work, nodes only transmit to the base station when it is close to them (or a neighbor). The goal is to compute a mobility path to collect data from visited nodes before those nodes suffer buffer overflows [7] , [8] , [14] , [15] . These approaches incur high latencies due to the low to moderate speed, e.g. 0.1-1 mls [14] , [16] , of mobile base stations.. Data mules are similar to the second form of mobile base stations [9] - [ 11] . Data mules pick up data from the sensors and transport it to the sink. In [20] , the data mule visits all the sources to collect data, transports data over some distance, and then transmits it to the static base station through the network. The goal is to find a movement path that minimizes both communication and mobility energy consumption. Similar to mobile base stations, data mules introduce large delays since sensors have to wait for a mule to pass by before starting their transmission.. In the third approach, the network consists of mobile relay nodes along with static base station and data sources. Relay nodes do not transport data; instead, they move to different locations to decrease the transmission costs. We use the mobile relay approach in this work. Goldenberg et al. [13] showed that an iterative mobility algorithm where each relay node moves to the midpoint of its neighbors converges on the optimal solution for a single routing path. However, they do not take into consideration the cost of moving the relay nodes. In [19] , mobile nodes decide to move only when moving is beneficial, (Le., mobility costs are covered by the savings in transmission costs). However, only the cost of moving to the midpoint of neighbors is considered in [19] .. Compared to the approaches of mobile base stations and data mules, our approach considers the energy consumption of both mobility and transmission, and requires much simpler motion planning. Specifically, after deployment, each mobile relay relocates only once and then remains stationary for data forwarding. The key difference between our approach and the mobile relay schemes in [13] and [19] is that we consider all possible locations as possible target locations for a mobile node instead of just its current position and the midpoint of its neighbors. Moreover, our approach accurately computes the optimal position of each mobile relay node.

O O O O O B I I O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Error characteristics and calibration-free techniques for wireless LAN-based location estimation Using wireless LAN technology for location estimation provides alternate means to enable location-based applications without investment in sensor network infrastructure and special hardware. However, the main drawback of wireless LAN-based location systems is calibration of signal strength as a function of location in spatially high-density, which consumes manual labor and needs to be carried out repeatedly. In this paper, we analyze empirical error characteristics of calibration-based location algorithms such as triangulation in various spatial densities of calibration, using commercially available wireless LAN products. Then, we propose Triangular Interpolation and eXtrapolation (TIX), a calibrationfree location algorithm, and present empirical performance evaluation. TIX can achieve mean distance error within 5.4 m, which is comparable to within 4.7 m errors of the calibrationbased algorithms. We also present theoretical analysis on error characteristics of the location algorithms deriving accuracy limits and quantifying the effect of RF measurement and calibration. Location information of a mobile user is regarded as a key requirement enabling new means to construct the future mobile applications and services. Due to poor indoor coverage of the Global Positioning System (GPS), indoor location estimation has been a challenging research issue. One approach for indoor location is to deploy infrared or ultrasound sensor network infrastructures. However, this approach is naturally concerned with investment cost, installation, and maintenance of sensor network infrastructure and special hardware. An alternate approach leverages the existing wireless LAN to enable RF-based location estimation as proposed in the previous literature such as [1, 2, 3, 4, 5, 6, 7, 8, 9] . Static scene analysis collectively refers to the latter approach.. Static scene analysis employs a number of wireless access points (APs) transmitting RF beacons. Using a wireless client as location sensor, received signal characteristics of an area covered by the location system are examined. However, t he main drawback of this approach is calibration of signal strength as a function location in spatially high-density, which consumes manual labor and needs to be carried out repeatedly. So far, few known work [6, 7] has addressed the issue of reducing calibration. Elimination of calibration, however, has not been addressed in any previous work and regarded as a very difficult research problem.. This paper discusses calibration-free techniques for wireless LAN-based indoor location estimation. In particular, we propose Triangular Interpolation and eXtrapolation (TIX) algorithm, which is a central part of our calibration-free techniques. Using commercially available IEEE 802.11b wireless LAN products, we obtained empirical error characteristics (or accuracy) of both calibration-based and calibration-free algorithms. Especially, we applied various spatial densities of calibration for calibrationbased classical algorithms. TIX achieved mean distance error within 5.4 m, which is 0.7 -1.4 m worse than densely-calibrated classical algorithms. We also present theoretical analysis on error characteristics of the location algorithms deriving accuracy limits and quantifying the effect of RF measurement and calibration.. Rest of the paper is organized as follows. Section 2 provides background of the work. Section 3 presents empirical error characteristics of calibration-based location estimation using classical algorithms. Section 4 introduces TIX algorithm, describes associated calibration-free techniques, and presents empirical error characteristics of calibration-free location estimation using TIX. Section 5 presents our theoretical analysis. In Section 6, we discuss related work and how our work differs from others. Finally, Section 7 concludes the paper. An o verview of our calibration-free location estimation techniques is depicted in Figure 4 , comprising the following steps:. 1. Location request: a mobile node (location client) requests location information to location system (location server) available online. We presented empirical error characteristics of the classical location algorithms in various spatial densities of calibration, and calibration-free TIX algorithm. TIX achieved mean distance error within 5.4 m with zero calibration, which is comparable to within 4.7 m errors of laborious calibration-based algorithms. Increasing calibration grid size for coarser granularity had gradual effect on estimation errors unless it was increased to a certain threshold. We presented theoretical analysis on error characteristics of location algorithms and validated key sources of errors in both calibration-based and calibration-free algorithms. Early work in wireless LAN-based location estimation included the RADAR [1] system. RADAR used KNN location algorithm in a static scene analysis framework. RADAR showed that fairly accurate indoor location could be estimated without a separate sensor network infrastructure. In their following work [ 2] , RADAR was enhanced by a Viterbi-like algorithm.. In [3] , an empirical work on a RADAR-like location system was presented. The authors adopted KNN location algorithm, which was used by RADAR, and experimented with various choices of K. They validated that choosing K > 3 (RADAR chose K = 3) did not improve the accuracy but degraded it by 5 -20 %.. Pandya et al. [4] presented the MultiLoc system, which utilizes information from multiple RF technologies to improve accuracy. The MultiLoc s ystem employs two simple 'sensor fusion' techniques to illustrate the benefit of using multiple technologies. In [5] , more sophisticated algorithm for sensor fusion, namely SELFLOC, was presented. The authors also showed that multiple estimation algorithms could be combined to further improve accuracy using SELFLOC.. Techniques described in [6] were one of the first location algorithms with reduced calibration. Triangulation Mapping Interpolation (TMI) algorithm could achieve smaller distance error than RADAR although TMI required smaller calibration table constructed from sparser grid space. Mapping and interpolation schemes based on signal processing algorithms were used. Krumm and Platt [7] presented a more experiment-oriented work in minimizing calibration for wireless LAN-based location systems. They showed a series of empirical estimation errors while varying amount of calibration with KNN algorithm. They also described an interpolation function for smoothing estimates with reduced amount of calibration.. Ladd et al. [8] developed a wireless LAN-based location system using Bayesian reasoning and a hidden Markov model. While it achieved fine accuracy (in 1 -2 m errors), very dense calibration is required. They acknowledged the extraordinary effort in calibration and suggested the use of robotics-based approach for it. Although Nibble [9] system was based on RF-based static scene analysis, it did not use any geometric location algorithms such as triangulation, but took a purely probabilistic approach (based on Bayesian network).. There are a number of other classes of location technologies. Ad hoc networking-based location systems, which require no calibration, typically impose other types of requirements such as certain degree of distribution of ad hoc users over an area covered by the location system. APS [10] is based on mixture of ad hoc routing, and range (e.g., ToA, TDoA) and angle (AoA) measurement technologies.. Our work differs from others in several aspects. First, we consider zero calibration. Location algorithms in [6, 7] considered reduced amount of calibration, but never eliminated it. TIX algorithm combined with our proposed calibration-free techniques only requires at least three APs in communicative range (25 -40 m), yet achieves comparable accuracy performance to those of calibration-based algorithms. We did not only empirically demonstrate how the impact of calibration, grid size, and use of location algorithms resulted in error characteristics of RF-based static scene analysis, but also qualitatively explained with theoretical analysis on the same parameters. To the best of our knowledge, such theoretical analysis is unprecedented in any previous literature of similar arts.

O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O B O O O B I O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O B I I O O O O O O O O O O O O O O O O O O B I I O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O B O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O B O O O O O O O O O O O O O B O O O O O O O O B O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O B O O O O O O O B O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O B O O O O O O O O O O O O O O O O O B I I O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Variable-Density Parallel Imaging With Partially Localized Coil Sensitivities Abstract-Partially parallel imaging with localized sensitivities is a fast parallel image reconstruction method for both Cartesian and non-Cartesian trajectories, but suffers from aliasing artifacts when there are deviations from the assumption of perfect localization. Such reconstructions would normally crop the individual coil images to remove the artifacts prior to combination. However, the sampling densities in variable-density -space trajectories support different field-of-views for separate regions in -space. In fact, the higher sampling density of low frequencies can be used to reconstruct a bigger field-of-view without introducing aliasing artifacts and the resulting image signal-to-noise ratio (SNR) can be improved. A novel, fast variable-density parallel imaging method is presented, which reconstructs different field-of-views from separate frequencies according to the local sampling density in -space. Aliasing-suppressed images can be produced with high SNR-efficiency without the need for accurate estimation of coil sensitivities and complex or iterative computations. The proposed method delivers fast, noniterative, and high-SNR autocalibrating parallel image reconstructions without introducing significant artifacts. While the image SNR is improved by utilizing larger s for low spatial frequencies, aliasing artifacts from high frequencies are suppressed by reducing this FOV. Furthermore, the gridding reconstruction and the subsequent combination of the individual images are straightforward processes with low computational complexity. The reconstruction speed of the proposed method will particularly benefit applications based on non-Cartesian acquisitions. In a variable-density acquisition, the denser sampling at low frequencies results in larger s compared with the periphery of -space. The proposed technique suppresses aliasing artifacts by reconstructing undersampled high-frequency data within a smaller region, . Meanwhile, the SNR efficiency is improved by retaining the low-frequency images in a larger extent, . Finally, individual coil images are SNR-optimally combined with weights computed from data-driven sensitivity estimates.. The PILS method utilizes the same for all data, and provides relatively faster and simpler reconstructions compared with the variable-FOV technique. The PILS images can be cropped to either or to remove aliasing artifacts or make more efficient use of the data, respectively. In contrast, the proposed method offers a favorable trade-off, and makes optimal use of the data in each -space partition without creating artifacts. As a result, it is also more robust against suboptimally localized sensitivities.. Because both PILS and the variable-FOV method utilize coil sensitivities as anti-aliasing filters, the acceleration limits are more heavily dependent on the coil configuration than for other techniques such as SENSE or GRAPPA, particularly for uniformly undersampled trajectories. Although these techniques can offer improved artifact-suppression at higher accelerations, they also suffer from noise amplification due to the corresponding -factors. It is important to note that regularization techniques can help improve the conditioning and the SNR of the SENSE reconstructions [39] . Nevertheless, because the proposed method does not embody a matrix inversion, it is more robust against suboptimal conditioning. For variable-FOV reconstructions, the SNR loss varies spatially depending on the portion of coils that contribute to the data reconstructed at each pixel.. While SENSE yields residual errors and artifacts in the absence of accurate sensitivity estimates, the proposed method is less sensitive to these inaccuracies. Although overweighting of low-or high-frequency data may cause localized blurring or increased noise respectively, such problems were not apparent for the reconstructions in this work. The autocalibrating SENSE and GRAPPA methods are also more tolerant to estimation errors, but the reconstructions normally incur considerable computational burden for non-Cartesian data. Contrarily, the proposed method assembles the final image with a pixel-wise linear combination following the simple gridding reconstruction and apodization steps. Therefore, the processing times are substantially reduced compared to the computationally-intensive approaches. To demonstrate the algorithm of the proposed method, component images reconstructed from separate -space partitions are displayed in Fig. 6 along with the combined image for a single coil and acceleration factors of 1.1, 2.3, 3.4, 4.5. For higher accelerations, the frequencies of samples in each partition are lowered, including the central segment but excluding the outermost. Although this reduces the resolution of the component images reconstructed from the inner segments, the aliasing artifacts are suppressed. Furthermore, the final image does not suffer from any resolution loss, as long as the remaining coils provide the missing high-frequency data at the edge of . Fig. 7 shows the SOS, SENSE, and variable-FOV reconstructions of the aforementioned data collected with 1.1, 2.3, 3.4, 4.5. Although the SOS images have severe aliasing, both SENSE and the variable-FOV method effectively suppress these artifacts. Meanwhile, SENSE suffers from -factor-related noise amplification at higher accelerations due to poor conditioning of the encoding matrix [6] . It is important to note that the variable-FOV method provides much shorter reconstruction times than the iterative SENSE method, as expected. Table I lists the reconstruction times at each acceleration factor, demonstrating up to an order of magnitude improvement with the proposed technique. Fig. 8 validates the improved artifact-suppression capability of the variable-FOV method compared with PILS at two acceleration factors, 1.7, 4.5. While the PILS images suffer from residual aliasing artifacts, the variable-FOV method reliably suppresses both the more structured and the noise-like aliasing from low and high frequencies, respectively. Furthermore, this method achieves improved SNR compared with a PILS reconstructions were performed with FOV supported by the highest sampling density. A moderately strong display windowing was applied to emphasize differences in the level of aliasing artifacts. In both a and b, the arrows pinpoint regions of residual artifacts in the PILS images. In contrast, the variable-FOV method reliably suppresses these artifacts. Because this method reduces noise-like aliasing from high-frequency data and uses optimal combination weights, it yields reduced noise appearance compared with PILS. PILS image using supported by the lowest sampling density, due to the optimal combination weights and the extended for low frequencies. Table II lists the level of improvement at each value of , and 31.1% higher SNR was measured on average in the variable-FOV images at 4.5.

O B I O O O O O O B I O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Personalized recommender system based on item taxonomy and folksonomy Item folksonomy or tag information is popularly available on the web now. However, since tags are arbitrary words given by users, they contain a lot of noise such as tag synonyms, semantic ambiguities and personal tags. Such noise brings difficulties to improve the accuracy of item recommendations. In this paper, we propose to combine item taxonomy and folksonomy to reduce the noise of tags and make personalized item recommendations. The experiments conducted on the dataset collected from Amazon.com demonstrated the effectiveness of the proposed approaches. The results suggested that the recommendation accuracy can be further improved if we consider the viewpoints and the vocabularies of both experts and users. Recommender system is an effective tool to deal with the issue of information overload. Besides users' item preferences that profiled with explicit or implicit ratings, how to profile users' topic preferences is very important [1] . Traditionally, the taxonomy or ontology of items or the content information of items is used to find users' topic preferences [1] . Item taxonomy is a set of controlled vocabulary terms or topics designed to describe or classify items. The advantages of taxonomy include: vocabulary are standard and controlled, having relationship information among concepts, well recognized as common knowledge, and independent with user communities. One limitation is that it does not reflect users' personal viewpoints or preferences information.. Different with item taxonomy, folksonomy is contributed by users. Folksonomy has distinctive advantages which include being given by users explicitly and proactively, reflecting users' topic preferences and personal viewpoints on item descriptions or classifications, having multiple functions such as organizing and sharing items, building networks, and expressing explicit opinions [6] . It becomes another important information source to find users' topic preferences [6] . However, since there is no restriction or boundary on selecting words for tagging items, the tags used by users are free-formed and contain a lot of noise such as semantic ambiguity, tag synonyms and personal tags [7] [9] . The tag quality [7] [8] [9] problem generates difficulties in improving the accuracy of item recommendations based on tags.. An important research question is that can we integrate item folksonomy and taxonomy to overcome the tag quality problem and benefit from both. Some pioneer work discussed how to hybrid taxonomy and folksonomy for knowledge organization [2] and navigation [3] . Very few work discussed how to use both information sources to find more accurate user topic preferences and make personalized item recommendations so far. In this paper, we propose to use both item folksonomy and taxonomy to make personalized item recommendations. In this paper, we proposed to integrate the item taxonomy developed by experts and the item folksonomy contributed by users to make personalized item recommendations. To reduce the noise of tags, we propose to find the related taxonomic topics and tags to represent the personalized semantic meaning of each tag for each individual user. Based on the tag representations, we proposed approaches to find related taxonomic topics and tags to represent the topics of each item and the topic preferences of each user. The experimental results suggest that after removing the noise of tags, the tag information can be used as quality user profiling and item content describing information source to boost the accuracy of item recommendations. Moreover, the results also suggest that integrating the standard item taxonomy vocabulary and users' personal vocabularies as well as the viewpoints of both experts and users on item descriptions/classifications can further improve the accuracy of item recommendations. Item taxonomy is one important traditional information source to find users' topic preferences [1] . The important recommendation approaches based on item taxonomy include the work of Ziegler [4] . However, the taxonomic topic weighting approach did not consider the popularity of each taxonomic topic. Currently, the existing recommender systems only used one kind of the two information sources. For example, the recommendation approaches based on item taxonomy [4] or tags [6] . Very few work discussed how to use both information sources to make personalized item recommendations. Our previous work [5] proposed to convert users' preferences to tags into users' preferences to taxonomic topics. However the folksonomy vocabulary and users' personal viewpoints were not considered to profile users' topic preferences and items' topic descriptions.

O O O O O O B O B O B O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O B O B O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B B O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O O O B O O O O O O B O O O O O O O O O O O O O B O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O B O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O B O O O O O O O O O O O O O O O O O


Difference sphere: an approach to near light source estimation We Acquiring the knowledge of light sources is crucial in computer vision as well as in computer graphics especially with the recent advent of image based rendering techniques. Once the parameters of light sources are obtained, the illumination information can be effectively utilized for manipulating shadows, highlights, or shading on real/virtual object in images. In this paper, we consider the problem of estimating several co-existing light sources from a single image using a pair of spheres whose surface has Lambertian property. In particular, we deal with near point light sources, besides directional light source and ambient light, so that the reality of manipulated images should be increased.. The problem of estimating illuminant directions arises in the context of shape from shading [1] and early work focused on recovering a single distant light source assuming Lambertian surface and uniform albedo of target object. See [2, 3] for a few example. Since, there have been successful attempts to recover a more general illumination description [4] . Marschner and Greenberg [5] propose a method for estimating directions and radiant intensities of a few light sources in a scene by a least-squares method for surface intensity functions. In [6] , Yang and Yuille also solve for a small number of light sources by exploiting the constraints by occluding boundary. As an extension, Zhang and Yang [7] introduce a technique for estimating directions and radiant intensities of multiple light sources. While they analyze a single image of a reference sphere with known shape and Lambertian reflectance model, Zhou and Kambhamettu [8] extract these properties using stereo images of a reference sphere with specular reflection. They estimate the directions by the positions of highlights and radiant intensities from shading. Also, Maki [9] utilizes multiple images of an object that is in motion for estimating the illuminant direction by observing the brightness variance derived on the object surface. However, none of these approaches have made account for near point light sources that have varying effect depending on the distance. Thus, regarding indoor scenes, further accurate characterization of lighting is desired.. Recently, Debevec [10] uses a specular sphere as a light probe for measuring the incident illumination. Despite the accuracy of the estimated irradiance, such a sphere might have strong inter-reflections with other objects especially if they are close, which brings into question its validity in estimating near light sources. Also, Sato et al. [11] explicitly measure the 3D lighting distribution using stereo omnidirectional images that are captured with a fish-eye lens, and judge the positions of light sources by matching the highlights in the images. While this complete system is capable of representing the effects of point light sources, the irradiance is computed by interpolation on the bases of those accurate ones at cameras' projection centers and it is still difficult to achieve estimation of light sources that are in proximal scene. To our knowledge the most closely related work to our proposition in this respect is that by Powell et al. [12] . They present a technique for calibrating the light source geometry by matching highlights on three spheres. With this geometric matching method, it is possible to estimate the position of a light source although the radiant intensity of the light sources is not available.. In this paper we propose a novel method for estimating parameters of light sources, i.e., ambient light, directional light sources, and in particular near point light sources in- cluding their radiant intensity. We employ a pair of reference spheres as a light probe and analyze gray level contours on the spherical surfaces so that 3D geometric and photometric properties of light sources can be characterized. Our key idea then is introducing the notion of difference sphere that we acquire by differencing two image regions of the reference spheres. We show that separate identification of multiple combined light sources is facilitated through the analysis of gray level contours on the difference sphere.. The sequel of the paper is composed as following. In Section 2 we define the lighting and reflectance model. While introducing the notion of difference sphere in Section 3, we discuss the characteristics of it in Section 4. Section 5 provides the description of our algorithm of light source estimation followed by the experimental results in Section 6. Finally the paper is summarized in Section 7. • We divide the contour lines into contour segments based on Feature 1'.

B I O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O


Analysis of Shortest Path Routing for Large Multi-Hop Wireless Networks In this paper, we analyze the impact of straight line routing in large homogeneous multi-hop wireless networks. We estimate the nodal load, which is defined as the number of packets served at a node, induced by straight line routing. For a given total offered load on the network, our analysis shows that the nodal load at each node is a function of the node's Voronoi cell, the node's location in the network, and the traffic pattern specified by the source and destination randomness and straight line routing. In the asymptotic regime, we show that each node's probability that the node serves a packet arriving to the network approaches the products of half the length of the Voronoi cell perimeter and the load density function that a packet goes through the node's location. The density function depends on the traffic pattern generated by straight line routing, and determines where the hot spot is created in the network. Hence, contrary to conventional wisdom, straight line routing can balance the load over the network, depending on the traffic patterns. In this paper, using geometric probability, we have developed an analytical model to study the performance of straight line routing for multi-hop wireless networks. Our analytical results show that the probability that a node relays a packet depends on the location of the node and the perimeter of the node's Voronoi cell. In the asymptotic region, the relaying probability at a node is approximated as the product of the half length of the perimeter of the node and the load density that the packet goes through the node's location. Both simulations and analysis show that the relay load over the network, imposed by straight line routing, depends on the model of the traffic pattern. Even if the system settings are identical and straight line routing is commonly adopted, the relay load induced by "random" traffic could be distributed differently over the network. This paradoxical result is a consequence of the famous Bertrand's paradox. Thus, in contrast to traditional belief, there are many scenarios in which straight line routing itself can balance the load over the network, and in such cases explicit load-balanced routing may not help mitigate the relaying load.

B O O O B O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O B I O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O B O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O O O O O B O O O O O O O


Image registration using Adaptive Polar Transform Image registration is an essential task in many image processing applications. Log-Polar transform (LPT) is a well known tool for image processing for its rotation and scale invariant properties. However it suffers from nonuniform sampling which makes it not suitable for the environment when registered images are altered or occluded. Inspired by LPT, this paper presents a new algorithm that addresses the problems of the conventional LPT while maintaining the invariant properties. We introduce Adaptive Polar Transform (APT) technique and an innovative matching mechanism that serve as image processing tool for recovering scale and rotation change of the registered image. Unlike the conventional LPT that focuses only at the fovea area of the registered image, our proposed APT gives even consideration to the entire image. Translation of the registered image is recovered with the new search scheme by using Gabor feature extraction to accelerate the localization procedure. The experimental results indicate that our proposed method outperforms conventional LPT in registering images that are altered or occluded. Image registration is an essential task in many image processing applications. The objective is to find geometric transformations of the registered image in the target image. These transformations include translation, scale, and rotation. Many works have been done in this area in the past 20 years [1, 2] . Recently Zokia et al [3] proposed an innovative image registration technique by using Log-Polar transform (LPT). The provided experiments indicate successful results in registering image patches taken from the same scene with different orientations or scales. LPT [3, 4] is a well known tool for image processing for its rotation and scale invariant properties. Scale and rotation in Cartesian coordinate appears as translation in the log-polar domain. This invariant properties provide significant advantage in registering images. However, LPT also suffers from the nonlinear and nonuniform sampling. With LPT, the matching mechanism focuses only on the fovea or central area while the peripheral area is given less consideration. This makes LPT not suitable for registering images that have been altered or occluded, especially at the area closed to fovea. Another problem of LPT is the high computational cost in the transformation process, which comes from the oversampling at the fovea in the spatial domain. Since no information is gained from oversampling, this computation is wasted. Our work is motivated by these problems of the conventional LPT. We introduce Adaptive Polar Transform (APT) technique in the spatial domain that gives even consideration to the entire image, requires less computational cost during transformation, and maintains invariant properties for image registration purposes. An innovative matching mechanism is introduced to recover rotation and scale change, and the new search scheme is presented for accelerating the search process. The experimental results indicate that our proposed method outperforms the conventional LPT in registering images that are altered or occluded.. The paper is organized as follows. In section 2, we introduce our proposed algorithm in detail. Experimental results are shown in section 3 including comparison to the conventional LPT. Finally, our work is summarized in section 4. Although LPT has been widely used in many image processing applications, it suffers from nonuniform sampling. Inspired by this fact, this paper presents a new algorithm, which is developed to address the problem of the conventional LPT. The proposed APT provides even sampling to the entire image and yields faster sampling than conventional transformations. The matching mechanism is designed for image registration purposes and used for extracting rotation and scale information of the registered image. The innovative search scheme based on invariant features is also proposed. Experimental results demonstrate that our proposed algorithm outperforms the conventional LPT and succeeds in registering images that are altered or occluded.

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Non Abelian bent functions Abstract Perfect nonlinear functions from a finite group G Let G and H be two finite groups (in multiplicative representation). Perfect nonlinear functions from G to H are those ideal functions f : G → H that match the less possible with the pattern of group homomorphism, i.e., such that for all nonzero α ∈ G and for all β ∈ H,. When G and H are both (finite-dimensional) vector spaces over Z 2 = {0, 1}, these functions, originally introduced by Nyberg [9] , exhibit the maximal resistance against the differential attack [1] . Also in the Boolean case, this notion is known to be equivalent to bent functions: f : Z . is the Fourier transform of φ : G → C (this time α.x is the dot-product in Z m 2 ). These functions, introduced by Rothaus [15] (see also [3] ), exhibit the maximal resistance against the linear attack [8] .. The equivalence between bentness and perfect nonlinearity has been recently extended by Carlet and Ding [2] and Pott [14] to the general case: f : G → H (where G and H are two finite Abelian groups) is perfect nonlinear if, and only if, for all α ∈ G and for all nonprincipal character χ of H,. where for φ : G → C, φ is its discrete Fourier transform (see Section 3.2) . In this paper, we exhibit the same kind of dual characterizations in the case where at least one of the two finite groups G and H is non Abelian. This gives a general equivalence between perfect nonlinearity and bentness. Actually the notion of bentness is defined to be equivalent to perfect nonlinearity in those non Abelian cases.. Outline of the paper Next section contains the general notations used in the paper. In Section 3 are recalled some of the main results on the duality of finite groups. In particular, we present several kind of Fourier transforms used in the new characterizations of perfect nonlinearity in the non Abelian cases. The notion of perfect nonlinearity is exposed in the general framework of finite groups in Section 4. Also in this section is given the dual characterization-i.e., the notion of bentnessof Carlet and Ding [2] and Pott [14] of perfect nonlinear functions in the Abelian groups setting. Finally our own results of non Abelian bentness are developed in Section 5.. This paper is dedicated to the establishment of a dual characterization of the concept of perfect nonlinearity-similar to the one given by Carlet and Ding [2] and Pott [14] concerning Abelian groups-in the non Abelian groups setting, using some harmonic analysis techniques. So in this section, we recall some basics about the duality of finite groups and the Fourier transform. Most of the definitions and results given in this section are well-known and can be found in any book on finite groups ( [4, 10] for instance).

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Loopback: exploiting collaborative caches for large-scale streaming Abstract-In this paper, we propose a Loopback approach in a two-level streaming architecture to exploit collaborative client/proxy buffers for improving the quality and efficiency of large-scale streaming applications. At the upper level we use a content delivery network (CDN) to deliver video from a central server to proxy servers. At the lower level a proxy server delivers video with the help of collaborative client caches. In particular, a proxy server and its clients in a local domain cache different portions of a video and form delivery loops. In each loop, a single video stream originates at the proxy, passes through a number of clients, and finally is passed back to the proxy. As a result, with limited bandwidth and storage space contributed by collaborative clients, we are able to significantly reduce the required network bandwidth, I/O bandwidth, and cache space of a proxy. Furthermore, we develop a local repair scheme to address the client failure issue for enhancing service quality and eliminating most required repairing load at the central server. For popular videos, our local repair scheme is able to handle most of single-client failures without service disruption and retransmissions from the central server. Our analysis and simulations have shown the effectiveness of the proposed scheme.Index Terms-Content distribution, peer-to-peer streaming, video streaming. The idea of client collaboration has been widely applied to file sharing and application level multicast for both live and on-demand video streaming services. Although collaboration schemes usually utilize client resources to efficiently reduce central server and network load, several issues have to be addressed, such as limited client upstream bandwidth and storage space, short contribution periods, and less reliable services. Several peer collaboration solutions have been proposed under various assumptions of peer capabilities.. In P2Cast [8] , a session is formed by clients arriving close in time, and an application-level forwarding tree is constructed for VoD service. The first client in a session receives a video directly from the server. Subsequent clients receive a base video stream from the server or from one of the preceding clients. In addition, the client also receives a patching stream from other clients within the session. Each client caches an initial portion of a video. A client may serve multiple peers simultaneously but it is only available for the duration of video playback.. In a CDN-P2P hybrid architecture [9] , a client is assumed to transmit data at a fraction of video playback rate. Hence, a client may receive video streams from multiple peers. Furthermore, a client may be available for a multiple of video playback duration so that it may service more peers. However, a client caches an entire video, which is a rather high requirement.. Peer unreliability is another key challenge in client collaboration. An early peer departure may cause playback disruptions that affect many peers. In P2Cast, such disruptions are prevented with playback delays and shifted forwarding. Similarly, in [10] live video playback is protected with time-shifted transmissions for video patching and initial buffering. CoopNet [11] addresses client failures with redundant data and distribution paths. The data redundancy is achieved with multiple description coding. Each client receives multiple description streams from a number of peers. The video content can be reconstructed from a subset of all these streams. Path redundancy is achieved with multiple application-level multicast trees, one for each video description.. Since live streaming systems are often supported through application-level multicast trees, efficient methods for building application-level multicast trees have been investigated in [11] - [15] . In such schemes, the selection of peers to service a request is critical. Given a number of candidates, a set of supplying peers for a new peer is selected based on bandwidth availability and some other network path characteristics, e.g., delay is used in P2Cast [8] . Promise based on CollectCast [16] exploits the properties of the underlying network, topology and performance, for selection of supplying peers. It uses a network tomography method to build a graph representing connectivity between candidate peers and the receiver. Each network segment is characterized by loss rate, available bandwidth and delay. A set of supplying peers and a set of standby peers are selected based on the collected information. The session is continuously monitored and a switch to another peer from a standby set is executed in case of a peer failure.. Our Loopback mechanism further exploits the idea of passing data along clients as proposed in chaining [17] . However, in chaining, a client may have to cache an entire video in the worst case, which is a rather high requirement for a common client. In Loopback, we assume that each client contributes only a limited buffer space for caching. In addition, the extended chaining scheme [17] reduces server resource usage by delaying the client service to extend the chain length. Thus, the improvement is achieved at the cost of an additional delay. In Loopback, each client starts receiving data immediately. The fundamental difference between chaining and Loopback is that not only client collaboration but also proxy servers play the key roles in our Loopback scheme.

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