Modeling uncertainties for passive microwave precipitation retrieval: evaluation of a case study

Physically based microwave spaceborne techniques for rainfall retrieval are usually trained by simulated cloud-radiation databases (CRDs) composed of cloud profiles and associated brightness temperatures (TBs). When generating the database, the evaluation of the associated modeling uncertainties is crucial for retrieval error estimation. However, this is extremely complex due to the large number of free parameters. In this work, a possible methodology for taking into account CRD-related modeling uncertainties is proposed. The methodology-fairly general-is here applied to a limited dataset (a cloud-model resolved numerical output of a tropical cyclone). The modeling errors are obtained from systematic TB sensitivity tests associated to several parameters: particle sizes, temperature, ice content, sea surface wind speed, viewing angle, footprint size, radiative transfer schemes, melting phase, and particle shape. TB uncertainties are eventually summarized in a modeling error covariance matrix representing the intrinsic variability of the generated CRD. For comparison with real observations, the TBs are simulated at the spatial resolution, viewing geometry and frequencies of the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI). The matrix is evaluated with respect to TMI data in terms of an indicator called database matching index. Since they are based on a single case study and suffer from the lack of direct coupling of the radiative transfer with the cloud-resolving model, the provided results should not be considered an exhaustive evaluation of cloud-radiation modeling errors. Nevertheless, they may be considered a valuable starting point for error characterization, since extensions to larger databases could definitely improve modeling error budgets.     

Analysis of a ridge waveguide using overlapping T-blocks

A T-block (TB) approach is proposed to analyze the dispersion relation of a ridge waveguide. The field representations of a TB are obtained with the Green's function and mode-matching technique. Rigorous, yet simple dispersion equations for symmetric and asymmetric ridge waveguides are presented using a superposition of overlapping TBs. The rapid convergence characteristics of the dispersion equation are illustrated in terms of the cutoff wavenumbers. A closed-form dispersion relation, based on a dominant-mode approximation, is shown to be accurate for most practical applications such as couplers, filters, and polarizer designs.     

Integration of ATM call admission control and link capacity controlby distributed neural networks

An adaptive call admission control using neural networks was recently proposed for asynchronous transfer mode (ATM) communications networks. The author proposes adaptive link capacity control using neural networks. Neural networks are trained to estimate the call loss rate from link capacity and observed traffic, and link capacity assignment is optimized by a random optimization method according to the estimated call loss rate. The integration of adaptive call admission control and adaptive link capacity control yields an efficient ATM traffic control system suitable for multimedia communication services with unknown traffic characteristics. Computer simulation results using a simple network model are also given to evaluate the accuracy and efficiency of the proposed method     

Linear Phase Networks With Hyperbolic Tangent Function and Their Applications

This paper describes several methods to realize passive and active networks. with linear phase frequency response applicable to the video signal processing circuit especially for the FM transmission system. The methods are based on employing the hyperbolic tangent function realized by using passive LC ladder networks. They are also based on a time base conversion technique which provides the zero phase network. Using these methods, video signal processing circuits with linear phase property such as pre-emphasis and de-emphasis networks for the FM transmission TV system are introduced.     

A scalable synchronization protocol for large scale sensor networks and its applications

Synchronization is considered a particularly difficult task in wireless sensor networks due to its decentralized structure. Interestingly, synchrony has often been observed in networks of biological agents (e.g., synchronously flashing fireflies, or spiking of neurons). In this paper, we propose a bio-inspired network synchronization protocol for large scale sensor networks that emulates the simple strategies adopted by the biological agents. The strategy synchronizes pulsing devices that are led to emit their pulses periodically and simultaneously. The convergence to synchrony of our strategy follows from the theory of Mirollo and Strogatz, 1990, while the scalability is evident from the many examples existing in the natural world. When the nodes are within a single broadcast range, our key observation is that the dependence of the synchronization time on the number of nodes N is subject to a phase transition: for values of N beyond a specific threshold, the synchronization is nearly immediate; while for smaller N, the synchronization time decreases smoothly with respect to N. Interestingly, a tradeoff is observed between the total energy consumption and the time necessary to reach synchrony. We obtain an optimum operating point at the local minimum of the energy consumption curve that is associated to the phase transition phenomenon mentioned before. The proposed synchronization protocol is directly applied to the cooperative reach-back communications problem. The main advantages of the proposed method are its scalability and low complexity.     

Amplitude based keyless optical encryption system using deep neural network

Double random phase encryption (DRPE) system is a simple and powerful encoding technique that consists of only two lenses and two random phase masks. However, there are many issues for applying to actual security systems such as phase acquisition, vulnerability to phase retrieval techniques, and data throughput. Although various extensions of DRPE have addressed each issue, there is no comprehensive solution. To tackle all the issues of DRPE, we propose a new amplitude-based DRPE (ADRPE) system using deep learning. The encoding is the same as the current ADRPE system, and the decoding is achieved by an inverse ADRPE system using convolution neural networks. Our system can achieve a real-time end-to-end encryption system without any additional optical devices and exposure of the keys. To demonstrate our method, we applied it to simulations with various datasets such as passwords, Quick-Response (QR) codes, and fingerprints.     

Time tracking error in direct-sequence spread-spectrum networks dueto coherence among signals

Data are presented which reveal a time synchronization error in CDMA (code division multiple access) spread-spectrum networks where mutual signal phase coherence is high among communicators. The error is not white noise but is, in fact, periodic with an amplitude, phase, and mean offset which appears to be related to a mixture of the carrier frequency, chip rate, and code frame rate. This periodicity is more evident as carrier and code phase coherence increases among participants in a network and high tracking accuracy is the goal. This has implications for future high-rate data communications and navigation networks in which errors may be attributed to local oscillator instabilities more than a transmission link. The data using a commercial modem suggest that improvements in local oscillator stabilities will improve coherence among network participants but will not necessarily reduce time synchronization errors     

Efficient computation of marginal reliability-importance forreducible+ networks

Marginal reliability importance (MRI) of a link with respect to terminal-pair reliability (TR) is the rate to which TR changes with the modification of the success probability of the link. It is a quantitative measure reflecting the importance of the individual link in contributing to TR of a given network. Computing MRI for general networks is an NP-complete problem. Attention has been drawn to a particular set of networks (reducible networks), which can be simplified to source-sink (2-node) networks via 6 simple reduction rules (axioms). The computational complexity of the MRI problem for such networks is polynomial bounded. This paper proposes a new reduction rule, referred to as triangle reduction. The triangle reduction rule transforms a graph containing a triangle subgraph to that excluding the base of the triangle, with constant complexity. Networks which can be fully reduced to source-sink networks by the triangle reduction rule, in addition to the 6 reduction rules, are further defined as reducible⁺ networks. For efficient computation of MRI for reducible⁺ networks, a 2-phase (2-P) algorithm is given. The 2-P algorithm performs network reduction in phase 1. In each reduction step, the 2-P algorithm generates the correlation, quantified by a reduction factor, between the original network and the reduced network. In phase 2, the 2-P algorithm backtracks the reduction steps and computes MRI, based on the reduction factors generated in phase 1 and a set of closed-form TR formulas. As a result, the 2-P algorithm yields a linearly bounded complexity for the computation of MRI for reducible⁺ networks. Experimental results from real networks and benchmarks show the superiority, by two orders of magnitude, of the 2-P algorithm over the traditional approach     

Provisioning Methods for Bit-Rate-Differentiated Services in Hybrid Optical Networks

This paper addresses the problem of routing and wavelength assignment of bit-rate-differentiated optical services in a hybrid network. Hybrid optical networks are composed of resources, such as fiber links and photonic/electronic switches, that vary in their capabilities and transmission qualities. These networks are also responsible for the realization of optical services with varying quality-of-service (QoS) guarantees. In such networks, it is required to have a cost-effective assignment of the optical and electronic resources to these services in order to maximize the revenue of the network operator. This paper deals with optical services that are defined according to their tolerance to transmission impairments. We first divide the provisioning problem into two phases: (1) routing and (2) wavelength assignment and regeneration reservation. In the routing phase, a set of k-routes are generated to select from in the second phase, where each route optimizes a specific aspect of the problem (e.g., number of hops, maximum accumulated noise, etc.). The second phase, using the information about the resources along each route, attempts at finding the best wavelength allocation on that route such that the signal quality meets the service-level agreement (SLA). The second phase also uses the minimum number of regenerator ports on intermediate nodes for the purpose of wavelength translation and signal clean-up. Comparisons of the above scheme with a probing-based method, reveal substantial enhancements to the blocking performance with a maximum running time increase of 60%. In addition, the use of multiple routes provides higher reduction in the blocking probability over single-routing schemes. Moreover, the proposed, non-pessimistic, provisioning approach has a major impact on reducing the regeneration budget of the network.     

Cascadability study for optical label swapping using synchronous phase modulation

We experimentally investigate the cascadability of optical label swapping using a synchronous phase modulation technique without wavelength conversion in a recirculating loop to emulate multihop networks. We find that the power penalties for both label and payload are below 1 dB at 10/sup -7/ bit-error rate after five hops. We also show that a system penalty can be maintained below 1 dB for an accumulated timing mismatch of 20% of bit period using synchronous phase modulation-based optical label swapping. The results show the potential to save up to 80% of wavelength converters in optical packet switched networks applications.     

Voice and Internet Multimedia in UMTS Networks

Voice telephony is the predominant service on today's cellular mobile networks, in terms of number of customers, revenues and network usage. However, it is difficult to predict how long this will be the case given the rising demand for new Internet multimedia services. It is therefore essential that 3rd generation (3G) mobile networks support a voice telephony service, but also that these networks are also capable of providing Internet multimedia services using the same technology.This paper provides an overview of how voice telephony is provided in the initial phase of the universal mobile telecommunications system (UMTS). It then describes how this is expected to evolve in later phases — so that voice telephony becomes one of a large number of multimedia services provided from a common Internet protocol-based mobile network.     

STOLAS: switching technologies for optically labeled signals

GMPLS-based labeled optical burst switching (LOBS) networks are being considered as the next-generation optical Internet. GMPLS includes wavelength switching next to label and fiber (space) switching. We present a new concept of optically labeling bursts of packets suitable for LOBS networks supported by GMPLS. It is based on angle modulation, which enables control information to modulate the phase or frequency of the optical carrier, while payload data are transmitted via intensity modulation (IM). In particular, the optical label is orthogonally modulated, with respect to the payload, using either frequency shift keying or differential phase shift keying. We present a performance analysis of the modulation schemes by means of simulations where the influence of the payload IM extinction ratio and laser linewidth are investigated. In addition, the transmission performance of an IM/FSK combined modulated signal is experimentally validated at 10 Gb/s, demonstrating at the same time an FSK label swapping operation. Finally, a suitable optical label-controlled switch design is proposed that takes advantage of these novel labeling techniques, and efficiently combines widely tunable, fast switching lasers and SOA-MZI wavelength converters with an arrayed waveguide grating router.     

Uplink performance of slow frequency-hop multiple-access networks using binary DPSK

The uplink performance of synchronous and asynchronous slow frequency-hop spread-spectrum multiple-access (SFHSS-MA) networks transmitting L bits per hop using binary differential phase shift keying (BDPSK) is analyzed under the additive white Gaussian noise (AWGN) and Rayleigh fading channels. Analytic expressions for the average conditional bit error probabilities given a hop is hit by K' interfering users are derived. Results show that SFHSS-MA networks using BDPSK achieve nearly twice the maximum normalized network throughput compared to networks using BFSK under both AWGN and Rayleigh fading channels.     

A wide-band circularly polarized antenna

The design construction and testing of a wide-band circularly polarized antenna suitable for ionospheric research is described. The antenna operates in the range 2 to 7 MHz. Simple design formulas are given for the required broad-band phase shifting networks. Broad-band dipole antennas are used and suitable "balancing networks" are developed to match these antennas to the phase shifting networks ever the frequency range. A satisfactory compromise solution is found to the problem of matching the networks to the receiver using a broad-band transformer. Measurements of the rejection ratio of the system show that it is always better than approximately 16:1 over the required frequency range.     

Measurement selection for parametric IC fault diagnosis

This article presents experimental results which show feedforward neural networks are well-suited for analog IC fault diagnosis. Boundary band data (BBD) measurement selection is used to reduce the computational overhead of the FFN training phase. We compare the diagnostic accuracy between traditional statistical classifiers and feedforward neural networks trained with various measurement selection criteria. The feedforward networks consistently perform as well as or better than the other classifiers in term of accuracy. Training using BBD consistently reduces the FFN training efforts without degrading the performance. Experimental results suggest that feedforward networks provide a cost efficient method for IC fault diagnosis in a large scale production testing environment.This work is supported by NSF-IUC CDADIC, Project 90-1.     

Modeling Chirp and Phase Inversion in Wavelength Converters based on Symmetrical MZI-SOAs for use in All-Optical Networks

All-optical wavelength conversion based on multi-section semiconductor optical amplifiers (SOAs) in a symmetrical Mach-Zehnder interferometer (SMZI) is modeled for use in optical networks. It incorporates an enhanced SOA model that is implemented using the time domain transfer matrix approach and hence the overall numerical model determines simultaneously the wavelength and gain parameters for the wavelength converter. The overall model accurately predicts the optimal conditions for the SMZI arrangement in order to achieve the best results for the chirp, the phase inversion and the converted probe signal power. It is also demonstrated that large chirp and mismatch of the phase inversion reduces the eye opening ratio (EOR) which can seriously affect the performance of the wavelength converter to be used as a sub-system component in all-optical networks.     

Lumped element networks for replacing sections of a buriedtransmission line

A buried transmission line formed by vertical conductors can function as a wave guiding structure in producing a part of the electromagnetic field distribution caused by a distributed source at the air-earth interface. Such a structure, when excited by an appropriate low-frequency source, is a viable EMP simulation technique for use with underground systems. In the developmental phase of such a technology, there exists a need to artificially elongate the buried line by using lumped element networks. In effect, such networks simulate the simulator plates and earth. The authors address such a network concept and its design considerations. The actual design, fabrication, and testing of an example network are also presented     

Securing reliable server pooling in MANET against byzantine adversaries

Reliable server pooling (rSerPool) is an architecture and a set of protocols allowing a service provider to run several servers that can reliably provide the same service. Should a particular server fail while providing its service, another server can efficiently replace it. This property is attractive not only for wired but also for wireless networks. However, the unique characteristics of mobile ad hoc networks (MANETs) bring serious reliability and security challenges to the application of rSerPool. In this paper, we perform a comprehensive investigation of the security of rSerPool in MANET against both server failures and, especially, Byzantine attacks. We formulate security requirements for rSerPool in MANET and design efficient, distributed, and survivable security solutions for both main phases of rSerPool: service discovery and service provision. Specifically, we secure the service discovery phase by using a secure multiple-dominating set creation protocol, and the service provision phase by using a novel type of threshold signature scheme. Both protocols address novel security goals and are of independent interest as they can find applications to other areas; most notably, the construction of a distributed and survivable public-key infrastructure in MANET.     

Multibeam Selection for Indoor MIMO Systems: Two Cases of Study

The performance of multiple-input multiple-output (MIMO) systems using beam selection is investigated in this paper. Based on the results of a channel sounding campaign carried out at the University of Manitoba for line-of-sight (LOS) and non-line-of-sight (NLOS) scenarios, it was possible to contrast the results of transmitter, receiver and joint beam selection in rich scattering environments. The channel was characterized in the 1-2.4 GHz frequency band with a multipath delay resolution better than 5.8 ns. The beam selection was performed by exhaustive search method. The results led us to important conclusions regarding the beam selection procedure and its potential to improve the indoor channel capacity. In LOS, the single input single output (SISO) system that favours the maximum power direction of arrival (DOA) maximizes the capacity. Capacity improvements are observed by increasing the number of receiver beams (RBs) only at high signal-to-noise ratios (SNRs) for omnidirectional transmission. The best performance in transmitter beam selection in LOS is observed by increasing the number of transmitter beams (TBs) for high SNRs. In the case of NLOS, the capacity performance is improved when more than a single beam is used in either, transmitter or receiver side. The joint transmitter-receiver beam selection exhibits best capacity performance only for large SNRs in LOS while the SISO systems outperforms any joint beam selection alternative for low SNRs. In contrast, in NLOS environments, the use of joint beam selection shows a constant capacity performance improvement starting from lower SNR than in the LOS case     

Charge Transportation and Chirality in Liquid Crystalline Helical Network Phases of Achiral BTBT-Derived Polycatenar Molecules

First examples of multichain (polycatenar) compounds, based on the π-conjugated [1]benzothieno[3,2-b]benzothiophene unit are designed, synthesized, and their soft self-assembly and charge carrier mobility are investigated. These compounds, terminated by the new fan-shaped 2-brominated 3,4,5-trialkoxybenzoate moiety, form bicontinuous cubic liquid crystalline (LC) phases with helical network structure over extremely wide temperature ranges (>200 K), including ambient temperature. Compounds with short chains show an achiral cubic phase with the double network, which upon increasing the chain length, is at first replaced by a tetragonal 3D phase and then by a mirror symmetry is broken triple network cubic phase. In the networks, the capability of bypassing defects provides enhanced charge carrier mobility compared to imperfectly aligned columnar phases, and the charge transportation is non-dispersive, as only rarely observed for LC materials. At the transition to a semicrystalline helical network phase, the conductivity is further enhanced by almost one order of magnitude. In addition, a mirror symmetry broken isotropic liquid phase is formed beside the 3D phases, which upon chain elongation is removed and replaced by a hexagonal columnar LC phase.