Paul Anthony Polakos

High-power HTS microstrip filters for wireless communication

The performance of narrowband microstrip filters with low insertion loss and high power-handling capabilities made from YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) high-temperature superconducting (HTS) thin films is presented. Results are shown for two different designs that were chosen to optimize the power-handling capability. Both filters have a 2-GHz center frequency and 5 poles that incorporate coupled resonators with 10-/spl Omega/ internal impedances. They were made on 5-cm-diameter LaAlO/sub 3/ substrates. Both designs use parallel-coupled feed lines to avoid current crowding, The first design includes backward- and forward-coupled filters, has 1% bandwidth, and has handled over 25 watts of input power at 10 K with less than 0.25 dB compression. The second design has 1.2% bandwidth and uses only forward-coupled resonators. The dissipation loss is less than 0.2 dB at 45 K and it has a third-order intercept of 62 dBm. Another similar filter handled 36 watts of power at 45 K with less than 0.15 dB compression across the passband. We have developed a technique to visualize the power dissipation of the filter by observing the bubbles created by the filter when submerged in liquid helium, showing areas with local defects or where the current distribution is at its peak value. We also discuss several planar high-power filter issues, including material selection and fabrication, device configuration trade-offs, filter structure optimization, and design approaches to maximize power-handling capacity.

The tradeoff between coverage and capacity in dynamic optimization of 3G cellular networks

For 3G cellular networks, capacity is an important objective, along with coverage, when characterizing the performance of high-data-rate services. In live networks, the effective network capacity heavily depends on the degree that the traffic load is balanced over all cells, so changing traffic patterns demand dynamic network reconfiguration to maintain good performance. Using a four-cell sample network, and antenna tilt, cell power level and pilot fraction as adjustment variables, we study the competitive character of network coverage and capacity in such a network optimization process, and how it compares to the CDMA-intrinsic coverage-capacity tradeoff driven by interference. We find that each set of variables provides its distinct coverage-capacity tradeoff behavior with widely varying and application-dependent performance gains. The study shows that the impact of dynamic load balancing highly depends on the choice of the tuning variable as well as the particular tradeoff range of operation.

911-NOW: A network on wheels for emergency response and disaster recovery operations

Public safety organizations increasingly rely on wireless communication technology to provide effective command, control, and communication during emergencies and disaster response operations. Since emergencies can vary in scale from day-to-day operations to large-scale and widespread catastrophic events, any previously deployed network infrastructure may not be able to handle the traffic load. Worse, the wireless infrastructure may be damaged or destroyed, as occurred during the events of 9/11 and Hurricane Katrina. The 911-network on wheels (911-NOW) solution is a novel portable cellular system based on base station routers (BSRs) that does not require any pre-existing wireless infrastructure and provides capacity and coverage on demand. It is an auto-configurable system with a fully integrated service architecture that can be deployed as a single-cell solution for local communication or be configured to operate as an ad hoc network of cells. This paper describes the 911-NOW vision and discusses some of the differentiating features such as auto-configuration, network management, wireless mesh networking, and interoperability with existing public safety systems. We also highlight some of the research challenges associated with mobile and rapidly deployable wireless networks. In particular we provide an overview of issues centered upon dynamic assignment and management of Internet Protocol (IP) addresses, online and real-time calculation and maintenance of routing information, mobility management, and dynamic configuration and optimization of radio parameters.

High power failure of superconducting microwave filters: Investigation by means of thermal imaging

We have investigated power handling of high‐temperature superconducting microstrip filters employing highly sensitive thermal imaging. At low power, the images show small heating effects localized to areas with high current densities (ΔT<0.5 K), consistent with the known surface resistance and simulations of the current distribution. The breakdown at high‐power levels, however, is always nucleated by a frequency independent local hot spot (T≳Tc). Scanning electron microscopy analysis of this area reveals a flaw in the superconducting material, presumably reducing the local critical current. The maximum power handling of these filters is, therefore, still open to improvement.

Dynamic optimization in future cellular networks

With multiple air-interface support capabilities and higher cell densities, future cellular networks will offer a diverse spectrum of user services. The resulting dynamics in traffic load and resource demand will challenge present control loop algorithms. In addition, frequent upgrades in the network infrastructure will substantially increase the network operation costs if done using current optimization methodology. This motivates the development of dynamic control algorithms that can automatically adjust the network to changes in both traffic and network conditions and autonomously adapt when new cells are added to the system. Bell Labs is pursuing efforts to realize such algorithms with research on near-term approaches that benefit present third-generation (3G) systems and the development of control features for future networks that perform dynamic parameter adjustment across protocol layers. In this paper, we describe the development of conceptual approaches, algorithms, modeling, simulation, and real-time measurements that provide the foundation for future dynamic network optimization techniques.

High-temperature superconducting microstrip filters with high power-handling capability

The performance of narrowband microstrip filters with low insertion loss and high power-handling capabilities made from YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) high-temperature superconducting (HTS) films is presented. Results are shown for two different novel designs that were chosen to optimize the power-handling capabilities. Both have a 2-GHz center frequency and 5-poles that incorporate coupled resonators with 10-/spl Omega/ internal impedances on 50-mm-diameter LaAlO/sub 3/ substrates. Both designs use parallel-coupled feed lines to avoid current crowding. The first design includes backward- and forward-coupled filters, has 1% bandwidth, and has handled over 25 watts of input power at 10 K with less than 0.25 dB compression. The second design has 1.2% bandwidth and use only forward-coupled resonators. The minimum insertion loss is less than 0.2 dB at 45 K, it has a third-order intercept of 62 dBm. Another similar filter handled 36 watts of power at 45 K with less than 0.15 dB compression across the passband. We have developed a technique to visualize the power dissipation of the filter by observing the bubbles created by the filter when submerged in liquid helium, showing areas with local defects or where the current distribution is at its peak value.<<ETX>>

The new paradigm for wireless network optimization: a synergy of automated processes and human intervention

With the evolution of wireless technologies, the optimization process for the radio access network has undergone a dramatic increase in complexity. This trend is driven by the introduction of multiple objectives for packet data services, the increasing network heterogeneity resulting from technology overlays, and the growing demand for nondisruptive optimization of operating networks. In a multidisciplinary effort, Bell Laboratories has developed a new optimization methodology that tackles these challenges using automated processes. We show that the paradigm shift toward automation requires the development of several interdependent algorithms each designed to cope with a particular optimization task. In the application described, human intervention proves indispensable; it demands a new kind of expertise that combines understanding of the automated processes with knowledge of network operation. Through examples we illustrate the variety of tasks that have to be automated and where guidance is needed through human control. The development of these automated processes is an important step toward dynamic optimization routines that are integrated into the network and adjust the network in a real-time manner.

Self-optimization of LTE networks utilizing Celnet Xplorer

In order to meet demanding performance objectives in Long Term Evolution (LTE) networks, it is mandatory to implement highly efficient, autonomic self-optimization and configuration processes. Self-optimization processes have already been studied in second generation (2G) and third generation (3G) networks, typically with the objective of improving radio coverage and channel capacity. The 3rd Generation Partnership Project (3GPP) standard for LTE self-organization of networks (SON) provides guidelines on self-configuration of physical cell ID and neighbor relation function and self-optimization for mobility robustness, load balancing, and inter-cell interference reduction. While these are very important from an optimization perspective of local phenomenon (i.e., the eNodeBs interaction with its neighbors), it is also essential to architect control algorithms to optimize the network as a whole. In this paper, we propose a Celnet Xplorer-based SON architecture that allows detailed analysis of network performance combined with a SON control engine to optimize the LTE network. The network performance data is obtained in two stages. In the first stage, data is acquired through intelligent non-intrusive monitoring of the standard interfaces of the Evolved UMTS Terrestrial Radio Access Network (E-UTRAN) and Evolved Packet Core (EPC), coupled with reports from a software client running in the eNodeBs. In the second stage, powerful data analysis is performed on this data, which is then utilized as input for the SON engine. Use cases involving tracking area optimization, dynamic bearer profile reconfiguration, and tuning of network-wide coverage and capacity parameters are presented.

Capacity estimation for growth planning of cellular networks in the presence of temporal and spatial traffic fluctuations

Mobile traffic patterns are subject to rapid fluctuations over time, hence making network growth planning a cumbersome task for cellular-network providers. We introduce a network capacity metric that captures both temporal and spatial traffic fluctuations, and that can be derived from hourly service measurements as used for network growth planning. In a simulation trial, we compare this new metric to traditional methods that derive network capacity from performance evaluations of daily busy-hour traffic or time-averaged cell-load levels. We show that in the presence of temporal and spatial traffic fluctuations, the traditional methods overestimate network capacity and incorrectly project the relative gains achieved through capacity enhancement measures such as cell-hardware upgrade or dynamic load-balancing features.

Increased transition temperature in in situ coevaporated YBa2Cu3O7−δ thin films by low temperature post‐annealing

In situ coevaporated YBa2Cu3O7−δ thin films have a slightly depressed transition temperature Tc, though they have excellent radio‐frequency surface resistance characteristics. These films consistently have less orthorhombic strain than laser ablated or post‐annealed films. Low temperature (320–420 °C) post‐annealing of in situ coevaporated films in 100 kPa of O2 raised Tc to values as high as 91.5 K with some increase in the orthorhombic strain. All measured thin films show less variation of Tc with orthorhombic strain than does bulk material.