An improved sapce phasor based current hysteresis controller with reduced switching frequency variations using variable parabolic bands

A current error space phasor based simple hysteresis controller is proposed in this paper to control the switching frequency variation in two-level pulsewidth-modulation (PWM) inverter-fed induction motor (IM) drives. A parabolic boundary for the current error space phasor is suggested for the first time to obtain the switching frequency spectrum for output voltage with hysteresis controller similar to the constant switching frequency voltage-controlled space vector PWM-based IM drive. A novel concept of online variation of this parabolic boundary, which depends on the operating speed of motor, is presented. A generalized technique that determines the set of unique parabolic boundaries for a two-level inverter feeding any given induction motor is described. The sector change logic is self-adaptive and is capable of taking the drive up to the six-step mode if needed. Steady-state and transient performance of proposed controller is experimentally verified on a 3.7-kW IM drive in the entire speed range. Close resemblance of the simulation and experimental results is shown.

Asymmetric Cooperation Among Relays with Linear Precoding

Fixed and mobile relays are used, among other applications, in the downlink of cellular communications systems. Cooperation between relays can greatly increase their benefits in terms of extended coverage, increased reliability, and improved spectral efficiency. In this paper, we introduce the fundamental notion of asymmetric cooperation. For this, we consider a two-phase transmission protocol where, in the first phase, the base station (BS) sends several available messages to the relays over wireless links. But, depending on the channel state and the duration of the BS transmission, not all relays decode all messages. In a second phase, the relays, which may now have asymmetric message knowledge, use cooperative linear precoding for the transmission to the mobile stations. We show that for many channel configurations, asymmetric cooperation, although (slighlty) sub-optimum for the second phase, is optimum from a total-throughput point of view, as it requires less time and energy in the first phase. We give analytical formulations for the optimum operating parameters and the achievable throughput, and show that under typical circumstances, 20-30% throughput enhancement can be achieved over conventional systems.

An Empirical Analysis of Heterogeneity in IEEE 802.11 MAC Protocol Implementations and its Implications

Wireless LAN (WLAN) market consists of IEEE 802.11 MAC standard conformant devices (e.g., access points (APs), client adapters) from multiple vendors. Certain third party certifications such as those specified by the Wi-Fi alliance have been widely used by vendors to ensure basic conformance to the 802.11 standard, thus leading to the expectation that the available devices exhibit identical MAC level behavior. In this paper, however, we present what we believe to be the first ever set of experimental results that highlight the fact that WLAN devices from different vendors in the market can have heterogeneous MAC level behavior. Specifically, we demonstrate with examples and data that in certain cases, devices may not be conformant with the 802.11 standard while in other cases, they may differ in significant details that are not a part of mandatory specifications of the standard. We argue that heterogeneous MAC implementations can adversely impact WLAN operations leading to unfair bandwidth allocation, potential break-down of related MAC functionality and difficulties in provisioning the capacity of a WLAN. However, on the positive side, MAC level heterogeneity can be useful in applications such as vendor/model level device fingerprinting.

A unification-based decision procedure for cryptographic protocol analysis

We present a sound and complete decision procedure for the bounded process cryptographic protocol insecurity problem, based on the notion of normal proofs [2] and classical unification. We also show a result about the existence of attacks with “high” normal cuts. Our proof of correctness provides an alternate proof and new insights into the fundamental result of Rusinowitch and Turuani [9] for the same setting.

An adaptive MAC protocol in MANETs: a democratic approach

Mobile ad-hoc networks (MANETs) have recently drawn significant research attention since they offer unique benefits and versatility with respect to bandwidth spatial reuse, intrinsic fault tolerance, and low-cost rapid deployment. This paper addresses the issue of delay sensitive realtime data transport in these type of networks. An effective QoS mechanism is thereby required for the speedy transport of the realtime data. QoS issue in MANET is an open-end problem. Various QoS measures are incorporated in the upperlayers of the network, but a few techniques addresses QoS techniques in the MAC layer. There are quite a few QoS techniques in the MAC layer for the infrastructure based wireless network. The goal and the challenge is to achieve a QoS delivery and a priority access to the real time traffic in adhoc wireless environment, while maintaining democracy in the resource allocation. We propose a MAC layer protocol called "FCP based FAMA protocol", which allocates the channel resources to the needy in a more democratic way, by examining the requirements, malicious behavior and genuineness of the request. We have simulated both the FAMA as well as FCP based FAMA and tested in various MANET conditions. Simulated results have clearly shown a performance improvement in the channel utilization and a decrease in the delay parameters in the later case. Our new protocol outperforms the other QoS aware MAC layer protocols.

An improved method for calculating activities from distribution equilibria

The method of Gibbs-Duhem integration suggested by Speiser et al. has been modified to derive activities from distribution equilibria. It is shown that, in general, the activities of components in melts with a common anion can be calculated, without using their standard Gibbs energies of formation, from eqUilibrium ratios and the knowledge of activities in the metal phase. Moreover, if systems are so chosen that the concentration of one element in the metal phase lies in the Henry's law region (less than 1 %), information on activities in the metal phase is not required. Conversely, activities of elements in an alloy can be readily calculated from equilibrium distribution ratios alone, if the salt phase in equilibrium contains very small amounts of one element. Application of the method is illustrated using distribution ratios from the literature on AgCI-CuCI, AgBr-CuBr, and CuDo.5 -PbD systems. The results indicate that covalent bonding and van der Waals repulsive interactions in certain types of fused salt melts can significantly affect the thermodynamic properties of mixing.

Improved utilisation of an HF transformer in DC–AC application

Power conversion using high frequency (HF) link converters is popular because of compact size and light weight of highfrequency transformer. This study focuses on improved utilisation of HF transformer in DC–AC applications. In practical application, the operating condition of the power converter deviates significantly from the designed considerations. These deviating factors are commutation requirements (dead-time, overlap), mismatch in device drops and presence of the fundamental frequency in load current. As a result, the HF transformer handles some amount of low-frequency components (including DC) other than desired HF components. This causes the operating point in B-H curve to shift away from its normal or idealised position and hence results poor utilisation of the HF transformer and unwanted losses. This study investigates the nature of the problem with experimental determination of approximate lumped parameter modelling and saturation behaviour (B-H curve) of the HF transformer. A simple closed-loop control algorithm with online tuning of the controller parameters is proposed to improve the utilisation of the isolation transformer. The simulation and experimental results are presented.

An improved X-ray structural analysis for determining cation distribution in ZnFe2O4 and ZnFe2O4- Fe3O4 solid solutions

The distribution of zinc cation between crystallographically nonequivalent positions in ZnFe204 has been determined by anomalous X-ray scattering near the Zn K absorption edge. Measured intensity ratio with two energies close to the edge can be quantitatively explained only by assigning all zinc cations to the tetrahedral position in the approximately cubic close packed array of oxygen ions. A similar conclusion has also been reached for ZnxFe3-x04 solid solutions with x = 0.73, 0.54 and 0.35 employing the improved X-ray method. This is consistent with the EXAFS results which indicate an almost unchanged environmental structure around zinc cation in these solid solutions.

H-DBUG: A High-level Debugging Framework for Protocol Verification using Assertions

The success of an ABV IP depends highly on the associated debugging environment. An efficient debugging environment helps the user to find out the exact location of the failure. Moreover, it provides information to the user in a refined detail of abstraction and permit adequate interaction. It has also been realized that adequate visualization support helps in tracking the behavioral aspects of the Design Under Test (DUT). Currently, the debugging tools provide information in the signal level and do not provide any information about the high-level behavior of the DUT. We present a debugging framework that takes the design specification, assertions and the user intent in a simple format and provides detailed information by processing the design trace on-line, or off-line. We also present a visualization framework to ease the debugging procedure. We have experimented with industrial standard on-chip bus protocols that ensure that this utility can be incorporated successfully in the present functional verification flow.