MEERA: Cross-Layer Methodology for Energy Efficient Resource Allocation in Wireless Networks

In many portable devices, wireless network interfaces consume upwards of 30% of scarce system energy. Reducing the transceiver's power consumption to extend the system lifetime has therefore become a design goal. Our work is targeted at this goal and is based on the following two observations. First, conventional energy management approaches have focused independently on minimizing the fixed energy cost (by shutdown) and on scalable energy costs (by leveraging, for example, the modulation, code-rate and transmission power). These two energy management approaches present a tradeoff. For example, lower modulation rates and transmission power minimize the variable energy component, but this shortens the sleep duration thereby increasing fixed energy consumption. Second, in order to meet the quality of service (QoS) timeliness requirements for multiple users, we need to determine to what extent each system in the network may sleep and scale. Therefore, we propose a two-phase methodology that resolves the sleep-scaling tradeoff across the physical, communications and link layers at design time and schedules nodes at runtime with near optimal energy-efficient configurations in the solution space. As a result, we are able to achieve very low run-time overheads. Our methodology is applied to a case study on delivering a guaranteed QoS for multiple users with MPEG-4 video over a slow-fading channel. By exploiting runtime controllable parameters of actual RF components and a modified 802.11 medium access controller, system lifetime is increased by a factor of 3-to-10 in comparison with conventional techniques.     

Monolithically integrated multi-wavelength laser by selective areagrowth with metal organic vapour phase epitaxy

A multiwavelength laser (MWL) is fabricated by means of selective area growth (SAG) with metal organic vapour phase epitaxy (MOVPE). The MWL consists of an array of amplifiers monolithically integrated with a transmissive (de-)multiplexer and to the author' knowledge, is the first device of the kind realised with only two growth step making use of SAG MOVPE     

Elliptic waveguide beam focusing and collimating elements in InP:analysis and experiment

A new waveguide focusing and collimating element which uses an elliptically shaped beam converter has been analysed and experimentally tested. The experimental results show good agreement with the designed values. These elements are index contrast insensitive and compact and only need simple waveguide technology     

III–V semiconductor waveguiding devices using adiabatic tapers

In the past few years much effort has been put into the fabrication and optimization of III–V semiconductor waveguiding devices with integrated adiabatic mode size converters (tapers). By integrating a taper with a waveguide device, one wants to reduce the coupling losses and the packaging cost of OEICs in future optical communication systems. This paper gives an overview of different taper designs, their performance and the technological approaches used in realizing such tapered devices.     

Magnetic flux pinning in epitaxial YBa2Cu3O7−δ thin films

The influence of microstructure on the critical current density of laser ablated YBa₂Cu₃O_7−δ thin films has been examined. Scanning tunneling microscopy was used to examine the morphologies of YBa₂Cu₃O_7−δ films and the morphology data were then correlated with measurements of the critical current density. The films were found to grow by an island nucleation and growth mechanism. The critical current densities of the films are similar to those of films with screw dislocation growth, indicating that screw dislocation growth is not necessary for good pinning. The data suggest that the critical current density in applied magnetic field may be higher in films with higher densities of growth features.     

Lattice-mismatched InGaAs layers grown by OMVPE on GaAs based compliant substrates

Thin GaAs compliant substrates have been developed in order to reduce the strain in lattice-mismatched layers during epitaxial overgrowth. Using OMVPE a variety of (30–80Å) thin GaAs layers were grown and successfully fused at 660°C on a host GaAs substrate with twist-angles between 10° and 45°. The resulting compliant substrates were overgrown with up to 3.6% lattice-mismatched and 1200 nm thick InGaAs layers. Nomarski phase contrast microscopy, photoluminescence and x-ray diffraction (XRD) were used to characterize the heteroepitaxial layers. The smooth and cross-hatch free morphology and the reduced DXRD peakwidth of the heteroepitaxial layers indicate a substantial improvement of the quality of heteroepitaxial material using compliant substrates.     

Models for Wireless Data Communications in Indoor Train Environment

The provisioning of wireless data services in the railway environment will become increasingly important for train operators and train constructors in the upcoming years. In this paper, we present models to predict train-to-wayside wireless data communications characteristics in terms of throughput, jitter, and packet loss predictions for 2G/3G networks. To this end, an extensive measurement campaign is carried out along a Belgian Intercity railway track. Based on these measurements, we apply a multiple regression, window mean, and autoregressive model. We find that the window mean model is recommended for the prediction of throughput and jitter, while the multiple regression model is more favorable for the prediction of packet loss. The implementation of these predictions in train-to-wayside communication systems can enhance the provisioning of seamless network connection necessary for a wide variety of data services.     

(Al)GaInP multiquantum well LEDs on GaAs and Ge

MOVPE growth of AlGaInP layers on GaAs and Ge have been demonstrated. The surface morphology of the epilayers was smooth under optimized growth conditions. The epilayers showed good PL intensity on both GaAs and Ge substrates. It has been observed that at room temperature the PL intensity drops in the first few seconds after excitation and attains a steady state. The Zn-doped AlGaInP did not show any signs of H-passivation. The MQW LEDs on both the substrates produced electroluminescence which increased with applied current. Results indicate the feasibility of AlGaInP LEDs on Ge.     

Adoption of Vehicular Ad Hoc Networking Protocols by Networked Robots

This paper focuses on the utilization of wireless networking in the robotics domain. Many researchers have already equipped their robots with wireless communication capabilities, stimulated by the observation that multi-robot systems tend to have several advantages over their single-robot counterparts. Typically, this integration of wireless communication is tackled in a quite pragmatic manner, only a few authors presented novel Robotic Ad Hoc Network (RANET) protocols that were designed specifically with robotic use cases in mind. This is in sharp contrast with the domain of vehicular ad hoc networks (VANET). This observation is the starting point of this paper. If the results of previous efforts focusing on VANET protocols could be reused in the RANET domain, this could lead to rapid progress in the field of networked robots. To investigate this possibility, this paper provides a thorough overview of the related work in the domain of robotic and vehicular ad hoc networks. Based on this information, an exhaustive list of requirements is defined for both types. It is concluded that the most significant difference lies in the fact that VANET protocols are oriented towards low throughput messaging, while RANET protocols have to support high throughput media streaming as well. Although not always with equal importance, all other defined requirements are valid for both protocols. This leads to the conclusion that cross-fertilization between them is an appealing approach for future RANET research. To support such developments, this paper concludes with the definition of an appropriate working plan.     

Mode evolution type polarization splitter on InGaAsP/InP

A new type of mode-evolution polarization-splitter based on InGaAsP/lnP has been designed and realized. The component uses the large waveguide birefringence of the first-order TE and TM modes in a ridge waveguide made in a heterostructure, In the input section an asymmetric Y-junction acts as a mode converter in order to inject first-order TE- and TM-modes in a polarization-splitting section, which consists of a Y-junction formed by a bimodal and a monomodal waveguide. In the output section a third Y-junction is connected to the bimodal waveguide to couple the first-order mode to a monomodal output waveguide. Components that are 6-mm long and show polarization splitting at a wavelength of 1.55 μm have been realized. The best splitting ratios are close to -20 dB, which is in agreement with BPM simulations. Excess losses are below 1 dB