Dynamic Host-Group/Multi-Destination Routing for Multicast Sessions

Multicast routing research efforts have mostly focused on supporting the host-group model in which multicast packets are addressed to a host (or multicast) group. Another multicast routing approach uses multi-destination addressing, where a multicast packet carries a list of the unique (unicast) addresses of all the group members. This form of routing can be accomplished using limited or no additional state beyond the existing unicast routing tables. It, therefore, scales well with the number of multicast sessions but does not scale well with the size of the multicast group and, in fact, requires the size of the multicast group to be below a certain threshold. In this paper, we envision a future scenario in which both host-group and multi-destination addressing routing approaches coexist within the Internet. We develop a dynamic routing context for this future scenario wherein a multicast session can adapt among different routing configurations depending on the number of multicast group members and how this number changes over time. We consider three routing options: (1) A single multi-destination addressed flow – suitable for small-group sessions, (2) multiple multi-destination addressed flows – suitable for medium-group sessions and (3) a single host-group addressed flow – suitable for large-group sessions. For multicast sessions that vary in group membership over time, different routing protocols may be best at different points in time. Our work is concerned with the development and evaluation of protocols that allow a multicast session to dynamically switch among these three routing options as the size of the session changes.     

Spatial-Temporal Cooperative Spectrum Sensing in Flat Fading Channels for Cognitive Radio Using Extend Kalman Filter

This paper investigates a new channel gain map tracking by Space-Time Extended Kalman Filtering (STEKF) for a flat channel, and a novel spectrum sensing via Time Spatial Weighted Non-negative Lasso (TSWNL) algorithm. STEKF enables CRs to estimate and interpolate channel gain map for the entire geographical area of interest with a limited number of CRs measurements. In order to sense primary users (PU) activities, include the transmission power by each PU, location and number of active PUs, TSWNL algorithm is proposed. Numerical results illustrate that the proposed STEKF channel estimation and TSWNL sensing algorithms outperforms linear methods.     

A novel high-speed CMOS circuit based on a gang of capacitors

There is no doubt that complementary metal-oxide semiconductor (CMOS) circuits with wide fan-in suffers from the relatively sluggish operation. In this paper, a circuit that contains a gang of capacitors sharing their charge with each other is proposed as an alternative to long N-channel MOS and P-channel MOS stacks. The proposed scheme is investigated quantitatively and verified by simulation using the 45-nm CMOS technology with V_DD = 1 V. The time delay, area and power consumption of the proposed scheme are investigated and compared with the conventional static CMOS logic circuit. It is verified that the proposed scheme achieves 52% saving in the average propagation delay for eight inputs and that it has a smaller area compared to the conventional CMOS logic when the number of inputs exceeds three and a smaller power consumption for a number of inputs exceeding two. The impacts of process variations, component mismatches and technology scaling on the proposed scheme are also investigated.     

High efficiency,high switching speed,AlGaAs/GaAs P-HEMT DC–DC converter for integrated power amplifier modules

This paper presents a high efficiency, high switching frequency DC–DC buck converter in AlGaAs/GaAs technology, targeting integrated power amplifier modules for wireless communications. The switch mode, inductor load DC–DC converter adopts an interleaved structure with negatively coupled inductors. Analysis of the effect of negative coupling on the steady state and transient response of the converter is given. The coupling factor is selected to achieve a maximum power efficiency under a given duty cycle with a minimum penalty on the current ripple performance. The DC–DC converter is implemented in 0.5 μm GaAs p-HEMT process and occupies 2 × 2.1 mm² without the output network. An 8.7 nH filter inductor is implemented in 65 μm thick top copper metal layer, and flip chip bonded to the DC–DC converter board. The integrated inductor achieves a quality factor of 26 at 150 MHz. The proposed converter converts 4.5 V input to 3.3 V output for 1 A load current under 150 MHz switching frequency with a measured power efficiency of 84%, which is one of the highest efficiencies reported to date for similar current/voltage ratings.     

Cell Selection for Load Balancing in Heterogeneous Networks

The vision of advanced long-term evolution (LTE-A) project is set to ultimate increase of network capacity in heterogeneous networks (HetNets). In HetNets with small cell configuration, a considerable majority of user devices is eventually connected to the macrocell base station (MBS), while small base stations (BSs), such as femtocell access points (FAPs), are still without any user. This results in unbalanced load and reduces the data rate of macrocell user equipment (MUE). In this paper, a method is proposed for load balancing among FAPs, while desired throughput is achieved. The proposed method uses the estimated received signal strength from different BSs and adjusted pilot signals. Under the critical signal to interference plus noise ratio (SINR) condition, a list of candidate FAPs is prepared. The updated candidate list henceforth does not include the least visited FAPs, which in turn leads to lower unnecessary handoffs. Once the BS with the highest number of free RBs and the highest pilot signal power is selected, FAP allocates the RBs with higher SINRs (qualified RBs) to user. In the case of FAP unavailability, the algorithm compels users to connect to the MBS with adequate qualified RBs. The performance of the proposed method was evaluated under a variety of FAPs density, and the number and velocity of users in terms of throughput and Jain’s fairness index. The results evidence affordable improvements in the throughput and Jain’s index in comparison with other methods.     

Closed‐Loop Transmit Diversity Techniques for Small Wireless Terminals and Their Performance Assessment in a Flat Fading Channel

Closed‐loop transmit diversity is considered an important technique for improving the link budget in the third generation and future wireless communication standards. This paper proposes several transmit diversity algorithms suitable for small wireless terminals and presents performance assessment in terms of average signal‐to‐noise ratio (SNR) and outage improvement, convergence, and complexity of operations. The algorithms presented herein are verified using data from measured indoor channels with variable antenna spacing and the results explained using measured radiation patterns for a two‐element array. It is shown that for a two‐element array, the best among the proposed techniques provides SNR improvement of about 3 dB in a tightly spaced array (inter‐element spacing of 0.1 wavelength at 2 GHz) typical of small wireless devices. Additionally, these techniques are shown to perform significantly better than a single antenna device in an indoor channel considering realistic values of latency and propagation errors.     

Efficiency Enhancement of Single‐Walled Carbon Nanotube‐Silicon Heterojunction Solar Cells Using Microwave‐Exfoliated Few‐Layer Black Phosphorus

Carbon nanotube‐silicon (CNT‐Si)‐based heterojunction solar cells (HJSCs) are a promising photovoltaic (PV) system. Herein, few‐layer black phosphorus (FL‐BP) sheets are produced in N‐methyl‐2‐pyrrolidone (NMP) using microwave‐assisted liquid‐phase exfoliation and introduced into the CNTs‐Si‐based HJSCs for the first time. The NMP‐based FL‐BP sheets remain stable after mixing with aqueous CNT dispersion for device fabrication. Due to their unique 2D structure and p‐type dominated conduction, the FL‐BP/NMP incorporated CNT‐Si devices show an impressive improvement in the power conversion efficiency from 7.52% (control CNT‐Si cell) to 9.37%. Our density‐functional theory calculation reveals that lowest unoccupied molecular orbital (LUMO) of FL‐BP is higher in energy than that of single‐walled CNT. Therefore, we observed a reduction in the orbitals localized on FL‐BP upon highest occupied molecular orbital to LUMO transition, which corresponds to an improved charge transport. This study opens a new avenue in utilizing 2D phosphorene nanosheets for next‐generation PVs.     

Radiation analysis and errors associated with the monopulse operation of a satellite direction finder

This work describes the radiation performance of a novel concept for direction and location finding, using stationary satellite beacons. The received signals are processed with a monopulse four-element array. The monopulse mode is generated using the phase excitation of the radiating elements. For accurate processing the radiation phase should correspond with the bearing angle around the boresight direction. Phase deviations, however, occur in this phase pattern owing to the discrete excitation of the elements. Therefore, detailed analyses are presented for this phase pattern, its attainable gain and the depolarization effects, in order to select the kind of array elements, and their spacings, which minimize the phase pattern deviations. The dipoles and the slots, as array elements, yield better phase performance, smaller size and simpler structures than horn radiators, at the expense of worse depolarization.     

A new quantum-dot cellular automata full-adder

A novel expandable five-input majority gate for quantum-dot cellular automata and a new full-adder cell are presented. Quantum-dot cellular automata (QCA) is an emerging technology and a possible alternative for semiconductor transistor based technologies. A novel QCA majority-logic gate is proposed. This component is suitable for designing QCA circuits. The gate is simple in structure and powerful in terms of implementing digital functions. By applying these kinds of gates, the hardware requirement for a QCA design can be reduced and circuits can be simpler in level, gate counts and clock phases. In order to verify the functionality of the proposed device, some physical proofs are provided. The proper functionality of the FA is checked by means of computer simulations using QCADesigner tool. Both simulation results and physical relations confirm our claims and its usefulness in designing every digital circuit.     

System effectiveness criteria for the analysis of MX basing modes

Due to the increased accuracy of the Soviet Strategic Rocket Forces, the present U.S. silo based missiles are becoming more vulnerable to attack. One reason for creating MX missiles in the first place is to avoid this vulnerability of silos. It is imperative now that basing of MX missiles be reconsidered before committing billions of dollars to a defensive system that may turn out to be a Maginot line for the 1980s. This paper puts forward criteria such as survivability, cost, operational readiness, technical feasibility, etc., and methodologies that can be used for the analysis and evaluation of various basing modes which might keep the deployment of MX missiles effective.