Some principles for designing a wide-area WDM optical network

We explore design principles for next-generation optical wide-area networks, employing wavelength-division multiplexing (WDM) and targeted to nationwide coverage. This optical network exploits wavelength multiplexers and optical switches in routing nodes, so that an arbitrary virtual topology may be embedded on a given physical fiber network. The virtual topology, which is used as a packet-switched network and which consists of a set of all-optical “lightpaths”, is set up to exploit the relative strengths of both optics and electronics-viz. packets of information are carried by the virtual topology “as far as possible” in the optical domain, but packet forwarding from lightpath to lightpath is performed via electronic switching, whenever required. We formulate the virtual topology design problem as an optimization problem with one of two possible objective functions: (1) for a given traffic matrix, minimize the network-wide average packet delay (corresponding to a solution for present traffic demands), or (2) maximize the scale factor by which the traffic matrix can be scaled up (to provide the maximum capacity upgrade for future traffic demands). Since simpler versions of this problem have been shown to be NP-hard, we resort to heuristic approaches. Specifically, we employ an iterative approach which combines “simulated annealing” (to search for a good virtual topology) and “flow deviation” (to optimally route the traffic-and possibly bifurcate its components-on the virtual topology). We do not consider the number of available wavelengths to be a constraint, i.e., we ignore the routing of lightpaths and wavelength assignment for these lightpaths. We illustrate our approaches by employing experimental traffic statistics collected from NSFNET     

Si/SiC-based DD hetero-structure IMPATTs as MM-wave power-source: a generalized large-signal analysis

A full-scale, self-consistent, non-linear, large-signal model of double-drift hetero-structure IMPATT diode with general doping profile is derived. This newly developed model, for the first time, has been used to analyze the large-signal characteristics of hexagonal SiC-based double-drift IMPATT diode. Considering the fabrication feasibility, the authors have studied the large-signal characteristics of Si/SiC-based hetero-structure devices. Under small-voltage modulation (～ 2%, i.e. small-signal conditions) results are in good agreement with calculations done using a linearised small-signal model. The large-signal values of the diode's negative conductance (5 × 10⁶S/m²), susceptance (10.4 × 10⁷ S/m^2}), average breakdown voltage (207.6 V), and power generating efficiency (15%, RF power: 25.0 W at 94 GHz) are obtained as a function of oscillation amplitude (50% of DC breakdown voltage) for a fixed average current density. The large-signal calculations exhibit power and efficiency saturation for large-signal (> 50%) voltage modulation and thereafter decrease gradually with further increasing voltage-modulation. This generalized large-signal formulation is applicable for all types of IMPATT structures with distributed and narrow avalanche zones. The simulator is made more realistic by incorporating the space-charge effects, realistic field and temperature dependent material parameters in Si and SiC. The electric field snap-shots and the large-signal impedance and admittance of the diode with current excitation are expressed in closed loop form. This study will act as a guide for researchers to fabricate a high-power Si/SiC-based IMPATT for possible application in high-power MM-wave communication systems.     

A novel delay-aware routing algorithm (DARA) for a hybrid wireless-optical broadband access network (WOBAN)

A hybrid wireless-optical broadband access network (WOBAN) is a promising architecture for future access networks. Recently, the WOBAN has been gaining increasing attention, and early versions are being deployed as municipal access solutions. This architecture saves on network deployment cost because fiber need not penetrate to each end user. However, a major research opportunity exists in developing an efficient routing algorithm for the wireless front-end of the WOBAN. We propose and investigate the characteristics of the delay-aware routing algorithm (DARA) that minimizes the average packet delay in the wireless front-end of a WOBAN. In DARA we model wireless routers as queues and predict wireless link states periodically. Our performance studies show that DARA achieves less delay and congestion, and improved load balancing compared to traditional approaches such as the minimum-hop routing algorithm, shortest-path routing algorithm, and predictive throughput routing algorithm.     

Quality-of-Service Based Protection in MPLS Control WDM Mesh Networks

Intelligent methods for automatic protection and restoration are critical in optical transport mesh networks. This paper discusses the problem of quality-of-service (QoS)-based protection in terms of the protection-switching time and availability for end-to-end lightpaths in a WDM mesh network. We analyze the backup lightpath-sharing problem in such networks and study the correlation of the working lightpaths and the impact of the correlation on the sharing of the backup lightpaths. We present a multi-protocol-label-switching (MPLS) control-based fully distributed algorithm to solve the protection problem. The proposed algorithm includes intelligent and automatic procedures to set up, take down, activate, restore, and manage backup lightpaths. It greatly reduces the required resources for protection by allowing the sharing of network resources by multiple backup lightpaths. At the same time, it guarantees, if possible, to satisfy the availability requirement even with resource sharing by taking the correlation of working lightpaths into consideration. A simple analysis of the proposed algorithm in terms of computation time and message complexity indicates that the implementation of the algorithm is practical. The illustrative studies that compare the performance of 1:1, unlimited sharing, and QoS-based backup sharing algorithms indicate that QoS-based sharing achieves comparable performance as unlimited sharing, which is much better than the 1:1 backup scheme in terms of connection blocking probability, average number of connections in the network for a given offered load, and network resource utilization.     

An Integrated Approach to Thermal Management in High-Level Synthesis

Thermal effects are becoming an important factor in the design of integrated circuits due to the adverse impact of temperature on performance, reliability, leakage, and chip packaging costs. Making all phases of the design flow aware of this physical phenomenon helps in reaching faster design closure. In this paper, we present an integrated approach to thermal management in architectural synthesis. Our synthesis flow combines temperature-aware scheduling and binding based on feedback from thermal simulation. We show that our flow is effective in preventing hotspot formation and creating an even thermal profile of the resources. Our integrated thermal management technique on average reduces the peak temperature of the resources by 7.34 degC when compared to a thermal unaware flow without increasing the number of resources across our set of benchmarks     

Bacteria-Responsive Self-Assembly of Antimicrobial Peptide Nanonets for Trap-and-Kill of Antibiotic-Resistant Strains

Bacterial trapping using nanonets is a ubiquitous immune defense mechanism against infectious microbes. These nanonets can entrap microbial cells, effectively arresting their dissemination and rendering them more vulnerable to locally secreted microbicides. Inspired by this evolutionarily conserved anti-infective strategy, a series of 15 to 16 residue-long synthetic β-hairpin peptides is herein constructed with the ability to self-assemble into nanonets in response to the presence of bacteria, enabling spatiotemporal control over microbial killing. Using amyloid-specific K114 assay and confocal microscopy, the membrane components lipoteichoic acid and lipopolysaccharide are shown to play a major role in determining the amyloid-nucleating capacity as triggered by Gram-positive and Gram-negative bacteria respectively. These nanonets displayed both trapping and killing functionalities, hence offering a direct improvement from the trap-only biomimetics in literature. By substituting a single turn residue of the non-amyloidogenic BTT1 peptide, the nanonet-forming BTT1-3A analog is produced with comparable antimicrobial potency. With the same sequence manipulation approach, BTT2-4A analog modified from BTT2 peptide showed improved antimicrobial potency against colistin-resistant clinical isolates. The peptide nanonets also demonstrated robust stability against proteolytic degradation, and promising in vivo efficacy and biosafety profile. Overall, these bacteria-responsive peptide nanonets are promising clinical anti-infective alternatives for circumventing antibiotic resistance.     

A Call-Admission Control (CAC) Algorithm for Providing Guaranteed QoS in Cellular Networks

Future broadband wireless access systems are expected to integrate various classes of mobile terminals (MTs), each class with a different type of quality of service (QoS) requirement. When the load on a wireless network is high, the guarantee of QoS for each class of MTs is a challenging task. This study considers two classes of MTs—profiled MTs and nonprofiled or regular MTs. It is assumed that profiled users require a guaranteed QoS. The measure of QoS is the probability of forced termination of a call that was allowed to access the network. Two previous handoff prioritization schemes—(i) prerequest scheme and (ii) guard channel scheme—decrease handoff failure (and hence forced termination). In this work, we compare and contrast both the schemes through extensive simulation and we find that neither guard channel nor channel prerequest scheme can guarantee a desired level of QoS for the profiled MTs. We then propose a novel call-admission control (CAC) algorithm that can maintain any desired level of QoS, while the successful call completion rate is very high. In the proposed algorithm, the new call arrival rate is estimated continuously, and when the estimated arrival rate is higher than a predetermined level, some new calls are blocked irrespective of the availability of channels. The objective of this new call preblocking is to maintain a cell's observed new call arrival rate at no more than the predetermined rate. We show that the proposed method can guarantee any desired level of QoS for profiled users.     

Path-protection routing and wavelength assignment (RWA) in WDM mesh networks under duct-layer constraints

This study investigates the problem of fault management in a wavelength-division multiplexing (WDM)-based optical mesh network in which failures occur due to fiber cuts. In reality, bundles of fibers often get cut at the same time due to construction or destructive natural events, such as earthquakes. Fibers laid down in the same duct have a significant probability to fail at the same time. When path protection is employed, we require the primary path and the backup path to be duct-disjoint, so that the network is survivable under single-duct failures. Moreover, if two primary paths go through any common duct, their backup paths cannot share wavelengths on common links. This study addresses the routing and wavelength-assignment problem in a network with path protection under duct-layer constraints. Off-line algorithms for static traffic is developed to combat single-duct failures. The objective is to minimize total number of wavelengths used on all the links in the network. Both integer linear programs and a heuristic algorithm are presented and their performance is compared through numerical examples.     

Protecting multicast sessions in WDM optical mesh networks

Recent advances in wavelength-division-multiplexing (WDM) technology are expected to facilitate bandwidth-intensive multicast applications. However, a single fiber (bundle) cut on such a network can disrupt the transmission of information to several destination nodes on a "light tree"-based multicast session. Thus, it is imperative to protect multicast sessions e.g., by reserving resources along backup trees. We show that, if a backup tree is directed-link-disjoint to its primary counterpart, then data loss can be prevented in the event of any single link failure. We provide mathematical formulations for efficient routing and wavelength assignment (RWA) of several multicast sessions (including their backup trees for dedicated protection) at a globally optimum cost. We present these formulations for networks equipped with two kinds of multicast-capable switch architectures: one using the opaque (O-E-O) approach and the other using transparent (all-optical) approach. We expand our formulations to accommodate sparse splitting constraints in a network, in which an optical splitter has limited splitting fanout and each node has a limited number of such splitters. We develop a profit-maximizing model that would enable a network operator to be judicious in selecting sessions and simultaneously routing the chosen ones optimally. We illustrate the solutions obtained from solving these optimization problem formulations for a representative-size network.     

Potential of asymmetrical Si/Ge and Ge/Si based hetero-junction transit time devices over homo-junction counterparts for generation of high power

Static and dynamic properties of both complementary n-Ge/p-Si and p-Ge/n-Si hetero-junction Double-Drift IMPATT diodes have been investigated by an advanced and realistic computer simulation technique, developed by the authors, for operation in the Ka-, V- and W-band frequencies. The results are further compared with corresponding Si and Ge homo-junction devices. The study shows high values of device efficiency, such as 23%, 22% and 21.5%, for n-Ge/p-Si IMPATTs at the Ka, V and W bands, respectively. The peak device negative conductances for n-Si/p-Ge and n-Ge/p-Si hetero-junction devices found to be 50.7 ? 10⁶ S/m² and 71.3 ? 10⁶ S/m², which are ～3-4 times better than their Si and Ge counterparts at the V-band. The computed values of RF power-density for n-Ge/p-Si hetero-junction IMPATTs are 1.0 ? 10⁹, 1.1 ? 10⁹ and 1.4 ? 10⁹ W/m², respectively, for Ka-, V- and W-band operation, which can be observed to be the highest when compared with Si, Ge and n-Si/p-Ge devices. Both of the hetero-junctions, especially the n-Ge/p-Si hetero-junction diode, can thus become a superior RF-power generator over a wide range of frequencies. The present study will help the device engineers to choose a suitable material pair for the development of high-power MM-wave IMPATT for applications in the civil and defense-related arena.