Comparison of nonlinear pulse interactions in 160-Gb/s quasi-linear and dispersion managed soliton systems

The understanding and development of 160-Gb/s transmission systems requires the study of the impact of different dispersion compensation schemes on pulse propagation in nonlinear fiber. In this paper, we present an investigation of 160-Gb/s optical transmission systems, focusing on optimal propagation regimes, and in particular, we analyze different transmission limitations and dominant nonlinear effects by comparing quasi-linear and dispersion managed soliton systems. Two quasi-linear systems, one using nonzero dispersion-shifted fiber (NZDSF) and the other single-mode fiber (SMF), and one short-period (1 km) dispersion managed soliton (DMS) system are studied, both for single-channel and wavelength-division-multiplexed (WDM) transmission. First, the performance of the two quasi-linear systems in single-channel transmission are compared and it is shown that the NZDSF and SMF systems allow similar error-free transmission distances with only small differences in the intrachannel four-wave mixing (IFWM) induced amplitude jitter. The effect of pulsewidth on transmission performance in this regime was investigated and the use of shorter pulses was found to result in lower amplitude jitter. We analyzed the behavior of the DMS system and showed that the reduced pulse broadening during transmission allowed a significantly longer single-channel transmission distance with a smaller impact of nonlinearities compared to quasi-linear propagation. The sensitivity of the DMS system performance to statistical fluctuations in the fiber dispersion was studied and the results show the level of accuracy in the dispersion management map which must be ensured in these systems. Finally, the performance of the DMS in WDM transmission was investigated and it was found that it was subject to very large penalties increasing the minimum channel spacing possible because of the strong impact of interchannel cross-phase modulation (XPM).     

AC-coupled front-end for biopotential measurements

AC coupling is essential in biopotential measurements. Electrode offset potentials can be several orders of magnitude larger than the amplitudes of the biological signals of interest, thus limiting the admissible gain of a dc-coupled front end to prevent amplifier saturation. A high-gain input stage needs ac input coupling. This can be achieved by series capacitors, but in order to provide a bias path, grounded resistors are usually included, which degrade the common mode rejection ratio (CMRR). This paper proposes a novel balanced input ac-coupling network that provides a bias path without any connection to ground, thus resulting in a high CMRR. The circuit being passive, it does not limit the differential dc input voltage. Furthermore, differential signals are ac coupled, whereas common-mode voltages are dc coupled, thus allowing the closed-loop control of the dc common mode voltage by means of a driven-right-leg circuit. This makes the circuit compatible with common-mode dc shifting strategies intended for single-supply biopotential amplifiers. The proposed circuit allows the implementation of high-gain biopotential amplifiers with a reduced number of parts, thus resulting in low power consumption. An electrocardiogram amplifier built according to the proposed design achieves a CMRR of 123 dB at 50 Hz.     

Three-dimensional encoding/two-dimensional decoding of medical data

We propose a fully three-dimensional (3-D) wavelet-based coding system featuring 3-D encoding/two-dimensional (2-D) decoding functionalities. A fully 3-D transform is combined with context adaptive arithmetic coding; 2-D decoding is enabled by encoding every 2-D subband image independently. The system allows a finely graded up to lossless quality scalability on any 2-D image of the dataset. Fast access to 2-D images is obtained by decoding only the corresponding information thus avoiding the reconstruction of the entire volume. The performance has been evaluated on a set of volumetric data and compared to that provided by other 3-D as well as 2-D coding systems. Results show a substantial improvement in coding efficiency (up to 33%) on volumes featuring good correlation properties along the z axis. Even though we did not address the complexity issue, we expect a decoding time of the order of one second/image after optimization. In summary, the proposed 3-D/2-D multidimensional layered zero coding system provides the improvement in compression efficiency attainable with 3-D systems without sacrificing the effectiveness in accessing the single images characteristic of 2-D ones.     

A Low-Complexity Multiuser Detector for Asynchronous CDMA QPSK Adaptive Antenna Array Systems

This paper proposes a low complexity joint space-time multiuser detection algorithm for asynchronous DS/CDMA antenna array systems. The proposed multiuser detector is composed of an adaptive antenna array, used as a linear beamformer, and a sliding window decorrelator. A QPSK modulation scheme is used in order to increase bandwidth efficiency. Numerical results are given in terms of Bit Error Rate (BER) under the assumption of a frequency-selective Rayleigh slow fading channel. In particular, the proposed receiver is shown to be near-far resistant, even in worst fading cases, and to exploit completely array introduction while maintaining acceptable computational complexity. The proposed architecture avoids linear filter realization of the decorrelator, which is impractical in the case of a large number of users, and operates with relatively short data frames instead of the complete information sequence. Finally, this receiver is very flexible to changes in timing configuration.     

A Novel Approach for Physical Layer Cryptography in Wireless Networks

Due to the enormous spreading of applied wireless networks, security is actually one of the most important issues for telecommunications. One of the main issue in the field of securing wireless information exchanging is the initial common knowledge between source and destination. A shared secret is normally mandatory in order to decide the encryption (algorithm or code or key) of the information stream. It is usual to exchange this common a priori knowledge by using a “secure” channel. Nowadays a secure wireless channel is not possible. In fact normally the common a priori knowledge is already established (but this is not secure) or by using a non-radio channel (that implies a waste of time and resource). The information is encrypted by means of a private key that must be known by both the transmitter and the receiver. One of the main weak point about security is the private key exchanging interval. The key cannot be public and cannot be known a priori. The problem is how to exchange this private key through a totally secure wireless channel. This contribution deals with the review of the main physical layer techniques for encrypting the information and the proposal of a new physical layer technique ensuring secure communication in a full wireless environment. The information is modulated, at physical layer, by the thermal noise experienced by the link between two terminals. A loop scheme is designed for unique recovering of mutual information. The probability of error/detection is analytically derived for the legal users and for the third unwanted listener (passive or active attacker). Both the case of passive and active attacks have also been implemented and simulated by using Matlab-Simulink software. The analytical results have been compared to the simulated ones. All the results show that the performance of the proposed scheme yields the advantage of intrinsic security, i.e., the mutual information cannot be physically demodulated (passive attack) or denied (active attack) by a third terminal.     

SPETA: Social pervasive e-Tourism advisor

Tourism is one of the major sources of income for many countries. Therefore, providing efficient, real-time service for tourists is a crucial competitive asset which needs to be enhanced using major technological advances. The current research has the objective of integrating technological innovation into an information system, in order to build a better user experience for the tourist. The principal strength of the approach is the fusion of context-aware pervasive systems, GIS systems, social networks and semantics. This paper presents the SPETA system, which uses knowledge of the user’s current location, preferences, as well as a history of past locations, in order to provide the type of recommender services that tourists expect from a real tour guide.     

Flexible Electronics: Thin Silicon Die on Flexible Substrates

Silicon thinned to 50 mum and less is flexible allowing the fabrication of flexible and conformable electronics. Two techniques have been developed to achieve this goal using thinned die: die flip chip bonded onto flexible substrates [polyimide and liquid crystal polymer (LCP)] and die flip chip laminated onto LCP films. A key to achieving each of these techniques is the thinning of die to a thickness of 50 mum or thinner. Conventional grinding and polishing can be used to thin to 50 mum. At 50 mum, the active die becomes flexible and must be handled by temporarily bonding it to a holder die for assembly. Both reflow solder and thermocompression assembly methods are used. In the case of solder assembly, underfill is used to reinforce the solder joints. With thermocompression bonding of the die to an LCP substrate, the LCP adheres to the die surface, eliminating the need for underfill.     

Performance evaluation of input and output queueing techniques inATM switching systems

Modeling alternatives for a fast packet switching system are analyzed. A nonblocking switch fabric that runs at the same speed as the input/output links is considered. The performance of the considered approaches are derived by theoretical analysis and computer simulations. Performance comparison between input queueing approaches with different selection policies are presented. Novel input and output queueing techniques are also proposed. In particular it is shown that, depending on the implementation, the input queueing approach studied in this paper achieves the same performance as the optimum (output) queueing alternative, without resorting to a faster packet switch fabric     

Field measurement of albedo for limited extent test surfaces

A new method is introduced for field measurement of surface albedo. This method consists of the use of a cylindrical shade ring made of opaque fabric with a known (low) albedo placed over a test surface. The albedo measurement is accomplished using two small pyranometers situated so that the downward-facing pyranometer receives radiation only from the test surface and the shade ring. The upward-facing pyranometer simultaneously records the incoming solar radiation. The radiation received by the downward-facing pyramometer is a combination of reflected radiation from shaded and unshaded portions of these two surfaces, requiring detailed accounting of the resulting view factor geometries. The method presented here improves upon past approaches by allowing for smaller sample sizes, minimizing errors associated with reflective properties of the surroundings, and allowing for accurate measurements even under partially cloudy skies. In addition to these methodological improvements we introduce an approach for estimating the uncertainty in the resulting albedo measurements. Results from field measurements are presented to validate the measurement protocol, and to compare its accuracy with the accuracy of a published standard.