Study of Capon method for array signal processing

The mean-square error (MSE) of Capon estimate of the directions-of-arrival (DOA) is established in the narrowband array processing case. An improved Capon-like DOA estimator is proposed and its MSE is studied as well. Performance comparisons between the standard and improved Capon DOA estimates, and between these two estimates and the linear prediction DOA estimate, are performed. It is concluded that the improved Capon-like method introduced in this paper provides more accurate DOA estimates in most cases.This work has been supported by the Swedish Research Council for Engineering Sciences under contract 91–676.     

Edge Provisioning and Fairness in VPN-DiffServ Networks

Customers of Virtual Private Networks (VPNs) over Differentiated Services (DiffServ) infrastructure are most likely to demand not only security but also guaranteed Quality-of-Service (QoS) in pursuance of their desire to have leased-line-like services. However, expectedly they will be unable or unwilling to predict the load between VPN endpoints. This paper proposes that customers specify their requirements as a range of quantitative services in the Service Level Agreements (SLAs). To support such services Internet Service Providers (ISPs) would need an automated provisioning system that can logically partition the capacity at the edges to various classes (or groups) of VPN connections and manage them efficiently to allow resource sharing among the groups in a dynamic and fair manner. While with edge provisioning a certain amount of resources based on SLAs (traffic contract at edge) are allocated to VPN connections, we also need to provision the interior nodes of a transit network to meet the assurances offered at the boundaries of the network. We, therefore, propose a two-layered model to provision such VPN-DiffServ networks where the top layer is responsible for edge provisioning, and drives the lower layer in charge of interior resource provisioning with the help of a Bandwidth Broker (BB). Various algorithms with examples and analyses are presented to provision and allocate resources dynamically at the edges for VPN connections. We have developed a prototype BB performing the required provisioning and connection admission.     

Guest Editorial: Special Issue on Performance Evaluation in Computer Vision

International Journal of Computer Vision -     

Fatigue of Lead Zirconate Titanate Ceramics II: Sesquipolar Loading

Piezoelectric actuators generally are driven with unipolar electric load cycles. Although the obtainable strain is increased by small excursions into the negative field regime, this type of load cycle is rarely considered, as its long-time reliability has been questioned. Here, we investigate the degradation of lead zirconate titanate during cycling between high positive and low negative electric fields. Measurements of the large and small signal parameters are used to quantify changes of the material. The fatigue behavior shifts from one best described with existing models of unipolar fatigue to bipolar-like fatigue with increasing field amplitude.     

Non-parametric convex identification of extended generalized Prandtl–Ishlinskii models

The Generalized Prandtl–Ishlinskii model (GPI) of hysteresis has wide applicability, partly because of its capability to model asymmetric hysteresis. It is characterized by three unknown functions. Today, GPI models are typically identified through trial and error by ad hoc methods, presuming parameterized expressions for these functions and then using nonlinear least squares to determine the parameters, with concurrent problems of convergence, a dependence on the initial parameter guess, and local minima. Except for the aggregated hysteresis input–output fit the result gives no information as to whether the functions chosen are appropriate or not. Here we present a method to circumvent these problems for a more general class of hysteresis models. First, we introduce an extended GPI model (XGPI), where an additional memoryless function is placed in parallel to the GPI model. This further widens the applicability, allowing, for example, arbitrary orientation of the hysteresis loop. For such models it is shown how its four separate mappings can be identified by convex optimization. Appropriate single-valued functions can then be fitted individually to the resulting mappings and, if necessary, the function parameters found can be fine-tuned using nonlinear least squares on input–output data. The method is applied to simulated data and experimental data from a magnetoelastic torque sensor, and the results are favorably compared to the results of another commonly used hysteresis model.     

Bipolar Fatigue Caused by Field Screening in Pb(Zr,Ti)O3 Ceramics

Bipolar cycling of lead zirconate titanate ceramics can lead to massive material damage in regions close to the electrode. The damaged region can be identified by color changes, and the microstructure in this region shows signs of interface melting. This damaged region can screen the sample volume from the applied voltages and reduced fields are applied to the undamaged part of the sample. This has two effects. The first one is that the bulk is effectively subjected to smaller fields, but the measured parameters are assigned to the applied field, yielding apparent fatigue curves. The second effect is that with further cycling, field screening protects the bulk of the sample from fatigue due to the reduced effective fields. If the damaged region is mechanically removed and the ferroelectric hystereses are measured again, nearly unfatigued parameters are obtained.     

Determinanten der Nutzungsbereitschaft von standortbezogenen Mobilfunkdiensten

This article develops 11 hypotheses on impacts of six customer characteristics on an individual??s willingness to use mobile location based services (LBS). Hypotheses are tested in a sample of 217 mobile communications customers in Germany who participated in a standardized online-survey. PLS analysis suggests that reported frequency of ??on the move?? information needs, perceived assessment of LBS in a customer??s social environment and extent of past use of other mobile data services have statistically as well as practically significant effects on adoption intentions for pull LBS. Data privacy risks and cost/bill size concerns are only weakly or not related to such intentions.