1,721,028 research outputs found
Coordination in a single-retailer two-supplier supply chain under random demand and random supply with disruption
Full text linkThis paper studies the coordination issue of a supply chain consisting of one retailer and two suppliers, a main supplier and a backup supplier. The main supplier’s yield is subject to disruption and the retailer faces a random demand. We determine the retailer’s optimal ordering policy and the main supplier’s production quantity that maximize expected profit of the centralized supply chain. We also analyze the decentralized scenario, and a combination of overproduction risk sharing and buy-back contracts with a side payment from/to the backup supplier is provided to coordinate the supply chain. Numerical examples are given to gain some qualitative insights.Fei Hu, Cheng-Chew Lim, Zudi Lu, and Xiaochen Su
Tracking mobile robot in indoor wireless sensor networks
Full text linkThis work addresses the problem of tracking mobile robots in indoor wireless sensor networks (WSNs). Our approach is based on a localization scheme with RSSI (received signal strength indication) which is used widely in WSN. The developed tracking system is designed for continuous estimation of the robot’s trajectory. A WSN, which is composed of many very simple and cheap wireless sensor nodes, is deployed at a specific region of interest. The wireless sensor nodes collect RSSI information sent by mobile robots. A range-based data fusion scheme is used to estimate the robot’s trajectory. Moreover, a Kalman filter is designed to improve tracking accuracy. Experiments are provided to assess the performance of the proposed scheme.Liping Zhang, Cheng-Chew Lim, Yiping Chen, and Hamid Reza Karim
A low-voltage operational amplifier with high slew-rate for sigma-delta modulators
No full textThis paper presents the design of a low-voltage operational amplifier suitable for sigma-delta (/spl Sigma//spl Delta/) modulator applications. The circuit technique is proposed to enhance the slew-rate performance and correspondingly can help to save the power of the amplifier. The simple circuitry of a current mirror is included with a degenerate resistor that can be selectively shunted. High-speed 2nd-order /spl Sigma//spl Delta/ modulators incorporating this technique is designed in a 0.18-/spl mu/m CMOS technology and power consumption can be saved more than 20% for a power supply voltage of 1.2V.Joongho Choi; Jinup Lim; Cheng Chew Li
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Verification of systems-on-chips using genetic evolutionary test techniques from a software applications perspective.
Full text linkThis thesis examines verification of system-on-a-chip (SoC) designs using a software applications test methodology that is enhanced by genetic evolutionary test generations and functional coverage.
The verification methodology facilitates application based testing using behavioural simulations before the chip is fabricated. The goal of the methodology is to verify commonly used real-life functionalities of the SoC earlier in the design process, so as to uncover design bugs that are considered most critical to actual SoC usages when the SoC is employed in its intended end-product. The verification methodology is based on a test building blocks approach, whereby many different components of various SoC application use-cases are extracted into building blocks, and then recomposed with other components to construct greater variety and range of test cases for verifying the SoC.
An important facet of the methodology is to address automated creation of these software application test cases in an effective and efficient manner. The goal is to maximise test coverage and hence bug detection likelihood using minimal verification resources and effort. To this end, test generations
techniques employing single and multi objective genetic algorithms and evolutionary strategies are devised in this thesis. Using coverage and test size to drive test generations, test suites which are continually evolved to enhance SoC verifications are created, thereby achieving automated coverage driven verifications.
Another enhancement for test generation is to select the input test creation parameters in an analytical manner. A technique using Markov chains is developed to model and analyse the test generation method, and by doing so, test parameters can be selected to achieve desired verification characteristics and outcomes with greater likelihood.
To quantify verification effectiveness, a functional coverage method is formulated. The coverage method monitors attributes of the SoC design during testing. The combinations of attribute values indicate the application functionalities carried out. To address the coverage space explosion phenomenon for such combinatorial methods and facilitate the coverage measurement process, partial order domains and trajectory checking techniques from the formal verification field of symbolic trajectory evaluation are adopted.
The contributions of this thesis are a verification platform and associated tool-suite that incorporates the software applications test methodology, algorithmic test generation, and functional coverage techniques.Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 201
Capacity of multiple-input multiple-output wireless communication systems operating in the HF band.
Full text linkSpatial multiplexing is a wireless communication technique that employs MIMO (multiple-input multiple-output) antenna arrays and spatial signal processing to effectively establish multiple parallel spatial data pipes within the same frequency band. The number of parallel spatial data pipes that can be supported is dependent on a number of factors, one of the most significant of these being multipath richness. In general, a channel that is rich in multipath will be capable of supporting a large number of parallel spatial data pipes, leading to high capacities.
The HF (high frequency) band is subject to significant multipath caused by multiple refractions and reflections between the ionospheric layers and the earth’s surface, making it a possible candidate for MIMO techniques. In this thesis, the capacity offered by spatial multiplexing in the HF band is investigated. To the best of our knowledge, no such investigation has previously been conducted. The approach taken involves collection of multi-channel HF sounder data from which antenna and propagating mode correlation measurements are made. The antenna and mode correlation measurements are used to generate stochastic channel matrices, from which estimates of MIMO capacity can be calculated.
The key contributions presented include estimation of HF MIMO capacity from ionograms, development of a multi-channel receiver for HF radio research, development of a model for the HF MIMO channel matrix, and development and application of a technique for estimating HF MIMO capacity from multi-channel receiver data. The results obtained from the investigation indicate that spatial multiplexing offers a significant increase in capacity compared with single channel communication technqiues, and should therefore be seriously considered for future HF radio systems. A major application that stands to benefit from HF MIMO technology is ship based communications.Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 201
Design and analysis of control schemes for soft real-time computation systems
Full text linkThis thesis studies the management of task execution percision in dynamic soft real-time computer systems which utilise imprecise computations. A Notice Generation (NG) approach is utilised to decide on task execution precision. We analyse four different NGs, with these four NGs at our disposal, six methods are proposed to deal with transient overload in the system. The overload is modelled by a significant increase in the mean arrival rate of tasks to the computation system. Results show that this method provides significant performance benefits over single scheme methods that ignore transient overloads.Thesis (M.Eng.Sc.) -- University of Adelaide, Dept. of Electrical and Electronic Engineering, 199
Random access schemes for multichannel communication and multipacket reception in wireless networks.
Full text linkRandom access schemes have used advanced capabilities of the physical layer to achieve reliable data transmissions over wireless communication channels. These capabilities include multichannel communication and multipacket reception. Incorporating the advanced capabilities into the access schemes, as a cross-layer design, is a challenging task because a more sophisticated approach is required to interface the physical layer and the medium access control (MAC) layer. This thesis presents development of research into the efficient random access schemes that provide a better set of cross-layer design approaches by taking into account the capabilities of multichannel communication and multipacket reception. The consideration is to propose multichannel random access schemes that use a channel outage concept of fading and interference. The system performance of the proposed schemes is then analysed. By considering imperfect channel information, a random backoff access scheme that operates with a channel sensing policy is developed. The sensing and access problem is formulated as a partially observable Markov decision process, and is solved with simple and efficient heuristic approaches. A new joint random access scheme that resolves packet collisions in the time and frequency domains is then proposed to enable effective uplink access. The joint scheme cooperates with a sensing method in which users are partially aware of channel conditions. With multipacket reception (MPR) capability, a new MAC protocol is developed by adopting a distributed access mechanism to support a wireless network in which MPR capable nodes coexist with non-MPR nodes.Thesis (Ph.D.) -- University of Adelaide, School of Electrical and Electronic Engineering, 201
Design study of energy-efficient routing protocol for wireless sensor networks.
Full text linkRecent advances in wireless sensor networks have led to an emergence of many routing
protocols. Limited battery capacity of sensor nodes makes energy efficiency a major and
challenge problem in wireless sensor networks. Thus, the routing protocols for wireless
sensor networks must be energy efficient in order to maximise the network lifetime.
In this thesis, we developed a centralised clustering, energy-efficient routing protocol
for wireless sensor networks. Our protocol consists of a cluster head selection algorithm,
a cluster formation scheme and a routing algorithm for the data transmission between
cluster heads and the base station. The cluster head selection algorithm is performed by
the base station using global information of the network. This algorithm aiming at choosing
cluster heads that ensure both the intra-cluster data transmission and inter-cluster
data transmission are energy-efficient. The cluster formation scheme is accomplished by
exchanging messages between non-cluster-head nodes and the cluster head to ensure a
balanced energy load among cluster heads. The routing algorithm is based on the optimal
transmission range for the data transmission between cluster heads and the base
station using multi-hop.
The performance of our routing protocol is evaluated by comparing with three existing
routing protocols on a simulation platform. The simulation results show that our
protocol can achieve better performance in terms of energy efficiency and network lifetime.
Because of the centralised algorithm and multi-hop routing, there is a small communication
overhead and transmission delay when using our protocol. Since our protocol can
save energy and prolong network lifetime, it is well suited for applications where energy
and network lifetime are the primary considerations and small overhead and time delay
can be tolerated.Thesis (M.Eng.Sc.) - University of Adelaide, School of Electrical and Electronic Engineering, 200
- …
