Distributed autonomous wireless channel assignment algorithm withpower control

Local autonomous dynamic channel allocation (LADCA) including power control is essential to accommodating the anticipated explosion of demand for wireless. The authors simulate call performance for users accessing channels in a regular cellular array with a base located at the center of each hexagon. The computer model includes stochastic channel demand and a propagation environment characterized by attenuation with distance as well as shadow fading. The study of LADCA shows that distributed power control and channel access can be combined in an access management policy that achieves satisfactory system capacity and provides desired call performance. The authors report: LADCA/power control is observed to be stable alleviating a major concern about users unaware of the signal to interference problems their presence on a channel might cause to others. There can be substantial inadvertent dropping of calls in progress caused by originating calls. Modeling user time dynamics is essential. LADCA contrasts very favorably with fixed channel allocation (FCA) in a comparative example     

An improved current-comparator-based 1000-A transconductanceamplifier for the in-situ calibration of transformer loss measuringsystems

A current comparator technique and an error feedforward control strategy are applied to the design of a high current transconductance amplifier to obtain a highly stable and accurate output current. The transconductance amplifier features a current output range of 1000 A with a compliance voltage of 3 V. It has the ability to provide a highly accurate current to a circuit that is operated at high voltage. This high-current transconductance amplifier is used in a system for the in-situ calibration of transformer loss measuring systems. The output current has accuracies of better than ±10 ppm (parts-per-million) in both magnitude and phase     

The WINLAB Network Centric Cognitive Radio Hardware Platform—WiNC2R

This paper presents the design goals and architecture of WiNC2R—the WINLAB Network Centric Cognitive radio hardware platform. The platform has been designed for flexible processing at both the radio physical layer and MAC/network layers with sustained bit-rates of ~10 Mbps and higher. The hardware prototype supports multi band operation with fast spectrum scanning, the ability to dynamically switch between a number of OFDM and DSSS modems and multiple MAC protocols. The radio modems, MAC, and network-layer protocols are implemented in a flexible manner using general-purpose processing engines and a set of dynamically configurable hardware accelerators. An FPGA based platform implementation currently in progress is described in terms of key hardware components including the software-defined modem, the flexible MAC engine and network-level processor. Preliminary prototyping results are reported, and a roadmap for further evolution of the WiNC2R board is provided.     

Comparison of double dosimetry algorithms for estimating the effective dose in occupational dosimetry of interventional radiology staff

'Double dosimetry' i.e. measurement with two dosemeters, one located above the protective apron and one under has been recommended in interventional radiology (IR) to determine the effective dose to staff. Several algorithms have been developed to calculate the effective dose from the readings of the two dosemeters, but there is no international consensus on what is the best algorithm. In this work, a few of the most recently developed algorithms have been tested in typical IR conditions. The effective dose and personnel dosemeter readings were obtained experimentally by using thermoluminescent dosemeters in and on a Rando-Alderson phantom provided with a lead apron. In addition, the effective dose and personnel dosemeter readings were calculated by the Monte Carlo method for the same irradiation geometry. The results suggest that most of the algorithms overestimate effective dose in the selected IR conditions, but there is also a risk of underestimation by using the least conservative algorithms. Two of the algorithms seem to comply best with the chosen criteria of performance, i.e. no underestimation, minimum overestimation and close estimation of effective dose in typical IR conditions. However, it might not be justified to generalise the results. It is recommended that whenever personnel doses approach or exceed the dose limit, IR conditions should be further investigated and the possibility of over- or under-estimation of effective dose by the algorithm used should be considered.     

Call blocking performance of distributed algorithms for dynamicchannel allocation in microcells

We determine the call blocking performance of channel-allocation algorithms where every channel is available for use in every cell and where decisions are made by mobiles/portables based only on local observations. Using a novel Erlang-B approximation method, together with simulation, we demonstrate that even the simplest algorithm, the timid, compares favorably with impractical, centrally administered fixed channel allocation. Our results suggest that an aggressive algorithm, that is, one requiring call reconfigurations, could provide a substantially reduced blocking probability. We also present some algorithms which take major steps toward achieving the excellent blocking performance of the hypothetical aggressive algorithm but having the stability of the timid algorithm     

A simple distributed autonomous power control algorithm and itsconvergence

For wireless cellular communication systems, one seeks a simple effective means of power control of signals associated with randomly dispersed users that are reusing a single channel in different cells. By effecting the lowest interference environment, in meeting a required minimum signal-to-interference ratio of ρ per user, channel reuse is maximized. Distributed procedures for doing this are of special interest, since the centrally administered alternative requires added infrastructure, latency, and network vulnerability. Successful distributed powering entails guiding the evolution of the transmitted power level of each of the signals, using only focal measurements, so that eventually all users meet the ρ requirement. The local per channel power measurements include that of the intended signal as well as the undesired interference from other users (plus receiver noise). For a certain simple distributed type of algorithm, whenever power settings exist for which all users meet the ρ requirement, the authors demonstrate exponentially fast convergence to these settings     

Using specially designed high-stiffness burnishing tool to achieve high-quality surface finish

This paper is focused on the process of ball burnishing. The influence of tool stiffness on surface roughness parameters was considered theoretically, while experimental investigation was conducted to establish the influence of initial surface roughness (previous machining) on the effects of ball burnishing as the finishing process. Experimental investigations were conducted over a wide interval of most influential process parameters (burnishing forces, burnishing feed, and number of burnishing passes). The material used in the experiments was aluminum alloy EN AW-6082 (AlMgSi1) T651. Burnishing was performed using a specially designed tool of high stiffness. Statistical analysis of experimental data revealed strong correlation between roughness, R _a, and burnishing force, burnishing feed, and number of passes for the three surfaces, each with different roughness parameters. Particular combinations of process parameters yielded very low surface roughness, R _a, equivalent to polishing. It is worth noting that high surface quality can be achieved with relatively small burnishing forces, which differs from the investigations published so far. Contrary to conventional approaches, which are based on elastic tool systems, the authors propose the burnishing process to be conducted with high-stiffness tools. Further investigation shall be focused on optimization of burnishing process parameters in order to achieve surface finish equivalent to high polish.     

Model testing of fixture–workpiece interface compliance in dynamic conditions

This paper is focused on the problem of compliance of interface between clamping/locating fixture elements and workpiece, under dynamic loads during machining. In contrast to previous investigations, the authors have developed a special device dedicated to testing of physical models which represent clamping/locating elements and workpiece. This device allows optimization of a large number of input parameters which are critical to interface compliance. It was used in experimental investigations to establish the impact that the radius of the spherical tip of a clamping/locating element has on the interface compliance and load capacity. The results of experimental investigation show that, under certain conditions, the clamping/locating elements with larger-radius spherical tips provide significantly lower interface compliance. Future investigations should be aimed at finding optimum macro- and micro-geometries of contact interface, as well as the selection of materials for clamping/locating elements.