Showing papers by "Alcatel-Lucent published in 2007"

Scaling learning algorithms towards AI

Abstract: One long-term goal of machine learning research is to produce methods that are applicable to highly complex tasks, such as perception (vision, audition), reasoning, intelligent control, and other artificially intelligent behaviors. We argue that in order to progress toward this goal, the Machine Learning community must endeavor to discover algorithms that can learn highly complex functions, with minimal need for prior knowledge, and with minimal human intervention. We present mathematical and empirical evidence suggesting that many popular approaches to non-parametric learning, particularly kernel methods, are fundamentally limited in their ability to learn complex high-dimensional functions. Our analysis focuses on two problems. First, kernel machines are shallow architectures, in which one large layer of simple template matchers is followed by a single layer of trainable coefficients. We argue that shallow architectures can be very inefficient in terms of required number of computational elements and examples. Second, we analyze a limitation of kernel machines with a local kernel, linked to the curse of dimensionality, that applies to supervised, unsupervised (manifold learning) and semi-supervised kernel machines. Using empirical results on invariant image recognition tasks, kernel methods are compared with deep architectures, in which lower-level features or concepts are progressively combined into more abstract and higher-level representations. We argue that deep architectures have the potential to generalize in non-local ways, i.e., beyond immediate neighbors, and that this is crucial in order to make progress on the kind of complex tasks required for artificial intelligence.

Bose-Einstein Condensation of Microcavity Polaritons in a Trap

Abstract: We have created polaritons in a harmonic potential trap analogous to atoms in optical traps. The trap can be loaded by creating polaritons 50 micrometers from its center that are allowed to drift into the trap. When the density of polaritons exceeds a critical threshold, we observe a number of signatures of Bose-Einstein condensation: spectral and spatial narrowing, a peak at zero momentum in the momentum distribution, first-order coherence, and spontaneous linear polarization of the light emission. The polaritons, which are eigenstates of the light-matter system in a microcavity, remain in the strong coupling regime while going through this dynamical phase transition.

Measurement of scattering rate and minimum conductivity in graphene.

Abstract: The conductivity of graphene samples with various levels of disorder is investigated for a set of specimens with mobility in the range of 1-20x10(3) cm2/V sec. Comparing the experimental data with the theoretical transport calculations based on charged impurity scattering, we estimate that the impurity concentration in the samples varies from 2-15x10(11) cm(-2). In the low carrier density limit, the conductivity exhibits values in the range of 2-12e2/h, which can be related to the residual density induced by the inhomogeneous charge distribution in the samples. The shape of the conductivity curves indicates that high mobility samples contain some short-range disorder whereas low mobility samples are dominated by long-range scatterers.

Combinators for bidirectional tree transformations: A linguistic approach to the view-update problem

Abstract: We propose a novel approach to the view-update problem for tree-structured data: a domain-specific programming language in which all expressions denote bidirectional transformations on trees. In one direction, these transformations---dubbed lenses---map a concrete tree into a simplified abstract view; in the other, they map a modified abstract view, together with the original concrete tree, to a correspondingly modified concrete tree. Our design emphasizes both robustness and ease of use, guaranteeing strong well-behavedness and totality properties for well-typed lenses.We begin by identifying a natural space of well-behaved bidirectional transformations over arbitrary structures, studying definedness and continuity in this setting. We then instantiate this semantic framework in the form of a collection of lens combinators that can be assembled to describe bidirectional transformations on trees. These combinators include familiar constructs from functional programming (composition, mapping, projection, conditionals, recursion) together with some novel primitives for manipulating trees (splitting, pruning, merging, etc.). We illustrate the expressiveness of these combinators by developing a number of bidirectional list-processing transformations as derived forms. An extended example shows how our combinators can be used to define a lens that translates between a native HTML representation of browser bookmarks and a generic abstract bookmark format.

Performance of Macro- and Co-Channel Femtocells in a Hierarchical Cell Structure

Abstract: In this paper, the feasibility of user deployed femtocells in the same frequency band as an existing macrocell network is investigated. Key requirements for co-channel operation of femtocells such as auto-configuration and public access are discussed. A method for power control for pilot and data that ensures a constant femtocell radius in the downlink and a low pre-definable uplink performance impact to the macrocells is proposed, and the theoretical performance of randomly deployed femtocells in such a hierarchical cell structure is analysed for one example of a cellular UMTS network using system level simulations. The resulting impact on the existing macrocellular network is also investigated.

Recent Advances on InAs/InP Quantum Dash Based Semiconductor Lasers and Optical Amplifiers Operating at 1.55 $\mu$ m

Abstract: This paper summarizes recent advances on InAs/InP quantum dash (QD) materials for lasers and amplifiers, and QD device performance with particular interest in optical communication. We investigate both InAs/InP dashes in a barrier and dashes in a well (DWELL) heterostructures operating at 1.5 mum. These two types of QDs can provide high gain and low losses. Continuous-wave (CW) room-temperature lasing operation on ground state of cavity length as short as 200 mum has been achieved, demonstrating the high modal gain of the active core. A threshold current density as low as 110 A/cm2 per QD layer has been obtained for infinite-length DWELL laser. An optimized DWELL structure allows achieving of a T0 larger than 100 K for broad-area (BA) lasers, and of 80 K for single-transverse-mode lasers in the temperature range between 25degC and 85degC. Buried ridge stripe (BRS)-type single-mode distributed feedback (DFB) lasers are also demonstrated for the first time, exhibiting a side-mode suppression ratio (SMSR) as high as 45 dB. Such DFB lasers allow the first floor-free 10-Gb/s direct modulation for back-to-back and transmission over 16-km standard optical fiber. In addition, novel results are given on gain, noise, and four-wave mixing of QD-based semiconductor optical amplifiers. Furthermore, we demonstrate that QD Fabry-Perot (FP) lasers, owing to the small confinement factor and the three-dimensional (3-D) quantification of electronic energy levels, exhibit a beating linewidth as narrow as 15 kHz. Such an extremely narrow linewidth, compared to their QW or bulk counterparts, leads to the excellent phase noise and time-jitter characteristics when QD lasers are actively mode-locked. These advances constitute a new step toward the application of QD lasers and amplifiers to the field of optical fiber communications

Tests of new physics from precise measurements of the Casimir pressure between two gold-coated plates

Abstract: A micromechanical torsion oscillator has been used to strengthen the limits on new Yukawa forces by determining the Casimir pressure between two gold-coated plates. By significantly reducing the random errors and obtaining the electronic parameters of the gold coatings, we were able to conclusively exclude the predictions of large thermal effects below $1\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ and strengthen the constraints on Yukawa corrections to Newtonian gravity in the interaction range from 29.5 nm to 86 nm.

Understanding Dynamic Spectrum Access: Models,Taxonomy and Challenges

Abstract: In last few years, especially after release of the FCC Spectrum Policy Task Force (SPTF)'s seminal report in 2002, we have witnessed growing interest in the field of Dynamic Spectrum Access (DSA) networks. Terms such as reconfigurable networks, Software Defined Radios (SDRs), Cognitive Radios and Cognitive Radio Networks (CRNs) have gained common use. Radio spectrum is a multidimensional entity; space, time, polarization, frequency, power of signal transmission and interference are some of the key dimensions. The static, command- and-control management of spectrum has led to barriers to accessing the spectrum in various dimensions. The notion of dynamic spectrum access can break these barriers in one or more of the dimensions. A review of published research in the technology, policy and legal facets of this broad area indicates that the community is addressing this problem from multitude of angles. In fact, we believe the situation is analogous to story of seven blind men attempting to describe an elephant based on what they perceive when they touch various parts of the elephant. As such, we contend that unless a clear taxonomy of various ways of dynamic access is developed, significant confusion can prevail within the community dealing with these new ways. This paper tries to rectify this situation. It aims to develop a clear taxonomy of various forms of DSA networks, describe in detail various models and identify required technology capabilities, architectural innovations and policy changes.

Frequency Estimation in Intradyne Reception

Abstract: We report on an optical intradyne receiver experiment with frequency estimation. Frequency estimation allows, if performed prior to block phase estimation or other phase recovery techniques, for a much higher frequency difference between transmit laser and local oscillator laser. We demonstrate the feasibility of our approach in a 20-Gb/s quadrature phase-shift keying experiment

Fairness and load balancing in wireless LANs using association control

Abstract: The traffic load of wireless LANs is often unevenly distributed among the access points (APs), which results in unfair bandwidth allocation among users. We argue that the load imbalance and consequent unfair bandwidth allocation can be greatly reduced by intelligent association control. In this paper, we present an efficient solution to determine the user-AP associations for max-min fair bandwidth allocation. We show the strong correlation between fairness and load balancing, which enables us to use load balancing techniques for obtaining optimal max-min fair bandwidth allocation. As this problem is NP-hard, we devise algorithms that achieve constant-factor approximation. In our algorithms, we first compute a fractional association solution, in which users can be associated with multiple APs simultaneously. This solution guarantees the fairest bandwidth allocation in terms of max-min fairness. Then, by utilizing a rounding method, we obtain the integral solution from the fractional solution. We also consider time fairness and present a polynomial-time algorithm for optimal integral solution. We further extend our schemes for the on-line case where users may join and leave dynamically. Our simulations demonstrate that the proposed algorithms achieve close to optimal load balancing (i.e., max-min fairness) and they outperform commonly used heuristics.

Evaluation of Transmit Diversity in MIMO-Radar Direction Finding

Abstract: It has been recently shown that multiple-input multiple-output (MIMO) antenna systems have the potential to dramatically improve the performance of communication systems over single antenna systems. Unlike beamforming, which presumes a high correlation between signals either transmitted or received by an array, the MIMO concept exploits the independence between signals at the array elements. In conventional radar, the target's radar cross section (RCS) fluctuations are regarded as a nuisance parameter that degrades radar performance. The novelty of MIMO radar is that it provides measures to overcome those degradations or even utilizes the RCS fluctuations for new applications. This paper explores how transmit diversity can improve the direction finding performance of a radar utilizing an antenna array at the receiver. To harness diversity, the transmit antennas have to be widely separated, while for direction finding, the receive antennas have to be closely spaced. The analysis is carried out by evaluating several Cramer-Rao bounds for bearing estimation and the mean square error of the maximum likelihood estimate

An Electrothermal Model for AlGaN/GaN Power HEMTs Including Trapping Effects to Improve Large-Signal Simulation Results on High VSWR

Abstract: A large-signal electrothermal model for AlGaN/GaN HEMTs including gate and drain related trapping effects is proposed here. This nonlinear model is well formulated to preserve convergence capabilities and simulation times. Extensive measurements have demonstrated the impact of trapping effects on the shapes of I(V) characteristics, as well as load cycles. It is shown that accurate modeling of gate-and drain-lag effects dramatically improves the large-signal simulation results. This is particularly true when the output loads deviate from the optimum matching conditions corresponding to real-world simulations. This new model and its modeling approach are presented here. Large-signal simulation results are then reported and compared to load-pull and large-signal network analyzer measurements for several load impedances at high voltage standing wave ratio and at two frequencies.

Network MIMO: Overcoming Intercell Interference in Indoor Wireless Systems

Abstract: Network MIMO is a family of techniques whereby each user in a wireless system is served through all the access points within its range of influence By tightly coordinating the transmission and reception of signals at multiple access points, network MIMO transcends the limits on spectral efficiency due to intercell interference Taking prior information- theoretic analyses of Network MIMO to the next level, this paper quantifies the spectral efficiency gains obtainable under realistic propagation and operational conditions Our study relies on detailed simulations and, for specificity, is conducted within the framework of the IEEE 80216e Mobile WiMAX system All the relevant physical-layer functionalities of Mobile WiMAX are accurately replicated Furthermore, to facilitate the coordination between access points, we postulate an indoor deployment organized around a gigabit-ethernet backhaul The results confirm that Network MIMO stands to provide a multiple-fold increase in spectral efficiency under such conditions

Terahertz quantum-cascade-laser source based on intracavity difference-frequency generation

Abstract: The terahertz spectral range (λ = 30–300 µm) has long been devoid of compact, electrically pumped, room-temperature semiconductor sources1,2,3,4. Despite recent progress with terahertz quantum cascade lasers2,3,4, existing devices still require cryogenic cooling. An alternative way to produce terahertz radiation is frequency down-conversion in a nonlinear optical crystal using infrared or visible pump lasers5,6,7. This approach offers broad spectral tunability and does work at room temperature; however, it requires powerful laser pumps and a more complicated optical set-up, resulting in bulky and unwieldy sources. Here we demonstrate a monolithically integrated device designed to combine the advantages of electrically pumped semiconductor lasers and nonlinear optical sources. Our device is a dual-wavelength quantum cascade laser8 with the active region engineered to possess giant second-order nonlinear susceptibility associated with intersubband transitions in coupled quantum wells. The laser operates at λ1 = 7.6 µm and λ2 = 8.7 µm, and produces terahertz output at λ = 60 µm through intracavity difference-frequency generation.

Effects of User-Deployed, Co-Channel Femtocells on the Call Drop Probability in a Residential Scenario

Abstract: The femtocell concept aims to combine fixed-line broadband access with cellular telephony using the deployment of low-cost, low-power 3G base stations in the subscriber's homes. These plug-and-play residential base stations would be deployed without much consideration to cell planning on the part of the user, relying instead on inbuilt auto-configuration abilities to minimise the impact on the macro cellular network by self-provisioning parameters such as the transmit and pilot power levels. In this paper, simulations of the deployment of such femtocells in a residential scenario were performed to study its effects on the service experienced by users that are connected to the underlay macrocells. The results show that with auto-configuration, the deployment of the femtocells would not pose a significant impact on the dropped call rate, causing an additional 0.45% increase in chance of a macrocell user's call dropping in the simulation's worst case scenario. In addition the impact of such femtocell deployment on the network signalling is discussed.

Decode-and-Forward Cooperative Diversity with Power Allocation in Wireless Networks

Abstract: We study power allocation for the decode-and-forward cooperative diversity protocol in a wireless network under the assumption that only mean channel gains are available at the transmitters. In a Rayleigh fading channel with uniformly distributed node locations, we aim to find the power allocation that minimizes the outage probability under a short-term power constraint, wherein the total power for all nodes is less than a prescribed value during each two-stage transmission. Due to the computational and implementation complexity of the optimal solution, we derived a simple near-optimal solution. In this near-optimal scheme, a fixed fraction of the total power is allocated to the source node in stage I. In stage II, the remaining power is split equally among a set of selected nodes if the selected set is not empty, and otherwise is allocated to the source node. A node is selected if it can decode the message from the source and its mean channel gain to the destination is above a threshold. In this scheme, each node only needs to know its own mean channel gain to the destination and the number of selected nodes. Simulation results show that the proposed scheme achieves an outage probability close to that for the optimal scheme obtained by numerical search, and achieves significant performance gain over other schemes in the literature

High accuracy bloom filter using partitioned hashing

Abstract: A method and system for generating a bloom filter by mapping into respective groups each of a plurality of initial keys according to a first hash function and mapping each group hashed key into a bloom filter using k respective hash functions.

A Wideband Spatial Channel Model for System-Wide Simulations

Abstract: A wideband space-time channel model is defined, which captures the multiple dependencies and variability in multicell system-wide operating environments. The model provides a unified treatment of spatial and temporal parameters, giving their statistical description and dependencies across a large geographical area for three outdoor environments pertinent to third-generation cellular system simulations. Parameter values are drawn from a broad base of recently published wideband and multiple-antenna measurements. A methodology is given to generate fast-fading coefficients between a base station and a mobile user based on the summation of directional plane waves derived from the statistics of the space-time parameters. Extensions to the baseline channel model, such as polarized antennas, are given to provide a greater variety of spatial environments. Despite its comprehensive nature, the model's implementation complexity is reasonable so it can be used in simulating large-scale systems. Output statistics and capacities are used to illustrate the main characteristics of the model

Scalable and embedded codec for speech and audio signals

Abstract: A system and method for processing of audio and speech signals is disclosed, which provide compatibility over a range of communication devices operating at different sampling frequencies and/or bit rates. The analyzer of the system divides the input signal in different portions, at least one of which carries information sufficient to provide intelligible reconstruction of the input signal. The analyzer also encodes separate information about other portions of the signal in an embedded manner, so that a smooth transition can be achieved from low bit-rate to high bit-rate applications. Accordingly, communication devices operating at different sampling rates and/or bit-rates can extract corresponding information from the output bit stream of the analyzer. In the present invention embedded information generally relates to separate parameters of the input signal, or to additional resolution in the transmission of original signal parameters. Non-linear techniques for enhancing the overall performance of the system are also disclosed. Also disclosed is a novel method of improving the quantization of signal parameters. In a specific embodiment the input signal is processed in two or more modes dependent on the state of the signal in a frame. When the signal is determined to be in a transition state, the encoder provides phase information about N sinusoids, which the decoder end uses to improve the quality of the output signal at low bit rates.

An introduction to PON technologies [Topics in Optical Communications]

Abstract: Passive optical networks are the most important class of fiber access systems in the world today. This article first reviews the reasons why the PON as a general architecture is so important. We then outline in some depth the technologies used to implement this architecture, including the G-PON and E-PON systems being deployed today, and the advanced PON systems that provide the evolution path to ever higher bandwidths

Message spoofing detection via validation of originating switch

Abstract: Message spoofing is detected by an anti-spoofing application comparing a trusted switch address (i.e., corresponding to an originating switch having processed an incoming message) to an 'affiliated' address (i.e., corresponding to a switch serving the location of the identified sender). Message spoofing is detected if the trusted address differs from the affiliated address.

A Multidimensional Framework for Understanding Outsourcing Arrangements

Abstract: SUMMARY The growth of outsourcing has resulted in numerous different outsourcing arrangements, ranging from out-tasking and managed services to business process outsourcing and transformational outsourcing. The growing lexicon of outsourcing terminology has caused confusion for many managers and academicians alike, who tend to view outsourcing as a fixed, discrete event or a simple make-or-buy decision. In reality, outsourcing is an umbrella term that includes a range of sourcing options that are external to the firm. Understanding these options, their characteristic differences, and how they serve to meet differing business objectives is the focus of the current research. Based on in-depth interviews with 19 senior executives experienced in outsourcing, as well as a thorough synthesis of available research, this article provides a framework clarifying the broad spectrum of outsourcing arrangements, and their inherent risks and advantages. Managerial guidance related to outsourcing is also provided.

Cross-talk and decision making in MAP kinase pathways.

Abstract: Cells must respond specifically to different environmental stimuli in order to survive. The signal transduction pathways involved in sensing these stimuli often share the same or homologous proteins. Despite potential cross-wiring, cells show specificity of response. We show, through modeling, that the physiological response of such pathways exposed to simultaneous and temporally ordered inputs can demonstrate system-level mechanisms by which pathways achieve specificity. We apply these results to the hyperosmolar and pheromone mitogen-activated protein (MAP) kinase pathways in the yeast Saccharomyces cerevisiae. These two pathways specifically sense osmolar and pheromone signals, despite sharing a MAPKKK, Ste11, and having homologous MAPKs (Fus3 and Hog1). We show that in a single cell, the pathways are bistable over a range of inputs, and the cell responds to only one stimulus even when exposed to both. Our results imply that these pathways achieve specificity by filtering out spurious cross-talk through mutual inhibition. The variability between cells allows for heterogeneity of the decisions.

Ims diameter router with load balancing

Abstract: A Diameter router (20) is presented for performing load balancing and initial Diameter message routing in an IMS network, where clients in network elements (10) are provisioned with the address of the router and send an initial Diameter request message (41) for a given session to the router. The router selects a server (31) based at least partially on a type of IMS message session, application services, subscriber information, or billing information, and sends a relayed initial Diameter request message (42) to the selected server. The selected server sends an initial Diameter response (43) to the router which then forwards a relayed initial response (44) to the client. Thereafter, the client and the selected server send messages directly to each other for the remainder of the session.

Provision of location-based services utilizing user movement statistics

Abstract: Location-based services are provided in a communication system comprising at least a portion of at least one wireless network. One aspect of the invention relates to generation of user movement statistics that may be utilized to facilitate the development of targeted marketing campaigns or other types of message delivery (e.g. advertisements or push messages). In this aspect, the user movement statistics are generated based on location and profile information for mobile user devices, and delivery of at least one message to a given one of the mobile user devices is controlled based on the user movement statistics. The user movement statistics may comprise, for example, information sufficient to determine approximately how many users having particular designated characteristics are likely to be in a given location at a given time, and may be utilized to determine prices charged for delivery of messages to the mobile user devices.

Network Coding-Based Broadcast in Mobile Ad-hoc Networks

Abstract: Broadcast operation, which disseminates information network-wide, is very important in multi-hop wireless networks. Due to the broadcast nature of wireless media, not all nodes need to transmit in order for the message to reach every node. Previous work on broadcast support can be classified as probabilistic (each node rebroadcasts a packet with a given probability) or deterministic approaches (nodes pre-select a few neighbors for rebroadcasting). In this paper, we show how network-coding can be applied to a deterministic broadcast approaches, resulting in significant reductions in the number of transmissions in the network. We propose two algorithms, that rely only on local two-hop topology information and makes extensive use of opportunistic listening to reduce the number of transmissions: 1) a simple XOR-based coding algorithm that provides up to 45% gains compared to a non-coding approach and 2) a Reed-Solomon based coding algorithm that determines the optimal coding gain achievable for a coding algorithm that relies only on local information, with gains up to 61% in our simulations. We also show that our coding-based deterministic approach outperforms the coding-based probabilistic approach presented in (C. Fragouli et al, 2006).

Phase-resolved measurements of stimulated emission in a laser.

Abstract: Laser radiation is usually measured with detectors that determine frequency and intensity, but gather no information about the phase of the radiation. By measuring the phase it would become possible to gain insights in the dynamic processes of optical amplification and attenuation underlying laser operation. Kroll et al. have now developed a way of measuring amplitude as well as phase of laser radiation from so-called quantum cascade lasers, which operate in the terahertz regime. The technique, which could be extended to other types of lasers, can be used to study effects leading to optical losses — useful information to improve the laser performance. Laser radiation is usually measured with intensity detectors that determine frequency and intensity, but throw away information about the phase of the radiation. But a scheme has been developed to measure amplitude as well as phase of laser radiation from so-called quantum cascade lasers, which operate in the terahertz regime. Lasers are usually described by their output frequency and intensity. However, laser operation is an inherently nonlinear process. Knowledge about the dynamic behaviour of lasers is thus of great importance for detailed understanding of laser operation and for improvement in performance for applications. Of particular interest is the time domain within the coherence time of the optical transition. This time is determined by the oscillation period of the laser radiation and thus is very short. Rigorous quantum mechanical models1,2 predict interesting effects like quantum beats, lasing without inversion, and photon echo processes. As these models are based on quantum coherence and interference, knowledge of the phase within the optical cycle is of particular interest. Laser radiation has so far been measured using intensity detectors, which are sensitive to the square of the electric field. Therefore information about the sign and phase of the laser radiation is lost. Here we use an electro-optic detection scheme to measure the amplitude and phase of stimulated radiation, and correlate this radiation directly with an input probing pulse. We have applied this technique to semiconductor quantum cascade lasers, which are coherent sources operating at frequencies between the optical (>100 THz) and electronic (<0.5 THz) ranges3. In addition to the phase information, we can also determine the spectral gain, the bias dependence of this gain, and obtain an insight into the evolution of the laser field.

Capacity for Classes of Broadcast Channels with Receiver Side Information

Abstract: Methods are developed that achieve all rate points inside the capacity region of two-receiver memoryless broadcast channels where each receiver knows the message it need not decode. The capacity result generalizes to channels with per-letter average cost constraints, e.g., additive white Gaussian noise channels with power constraints. The result further generalizes to cases where the receivers have only partial message information and where one receiver must decode both messages.

Coordinating Base Stations for Greater Uplink Spectral Efficiency in a Cellular Network

Abstract: We propose an ambitious approach towards lifting the limits imposed by cochannel interference on the uplink spectral efficiency of a cellular network, viz., coordinating several base stations in the reception of users within their coverage area, and suppressing interference between users by means of coherent linear beamforming across the base stations. We evaluate by simulation the potential gain in spectral efficiency from such coordination, when there is 1 user per base station antenna in the network, and all users (but for a small fraction in outage) must be served at a constant and common data rate. We highlight the dependence of the spectral efficiency gain on the number of rings of neighbors with which each base station is coordinated, as well as the underlying signal-to-noise ratio (SNR) distribution in the network. Results from this study point to the possibility of doubling the uplink spectral efficiency with 1-ring coordination and nearly quadrupling it with 4-ring coordination, under high-SNR conditions.