A wide axial-ratio beamwidth circularly-polarized oval patch antenna with sunlight-shaped slots for gnss and wimax applications

Wireless Networks - This paper proposes a quadruple band stacked oval patch antenna with sunlight-shaped slots supporting L1/L2/L5 GNSS bands and the 2.3 Ghz WiMAX band. The antenna produces...     

Scheduling with accurate communication delay model and scheduler implementation for multiprocessor system-on-chip

In multiprocessor system-on-chip, tasks and communications should be scheduled carefully since their execution order affects the performance of the entire system. When we implement an MPSoC according to the scheduling result, we may find that the scheduling result is not correct or timing constraints are not met unless it takes into account the delays of MPSoC architecture. The unexpected scheduling results are mainly caused from inaccurate communication delays and or runtime scheduler’s overhead. Due to the big complexity of scheduling problem, most previous work neglects the inter-processor communication, or just assumes a fixed delay proportional to the communication volume, without taking into consideration subtle effects like the communication congestion and synchronization delay, which may change dynamically throughout tasks execution. In this paper, we propose an accurate scheduling model of hardware/software communication architecture to improve timing accuracy by taking into account the effects of dynamic software synchronization and detailed hardware resource constraints such as communication congestion and buffer sharing. We also propose a method for runtime scheduler implementation and consider its performance overhead in scheduling. In particular, we introduce efficient hardware and software scheduler architectures. Furthermore, we address the issue of centralized implementation versus distributed implementation of the schedulers. We investigate the pros and cons of the two different scheduler implementations. Through experiments with significant demonstration examples, we show the effectiveness of the proposed approach.     

Design and development of dynamic Agri-ontology for IoT interoperability

In recent years, the usage and applications of Internet of Things (IoT) have increased exponentially. IoT connects multiple heterogeneous devices like sensors, micro controllers, actuators, smart devices like mobiles, watches, etc. IoT contributes the data produced in the context of data collection, including the domains like military, agriculture, healthcare, etc. The diversity of possible applications at the intersection of the IoT and the web semantics has prompted many research teams to work at the interface between these two disciplines. This makes it possible to collect data and control various objects in transparent way. The challenge lies in the use of this data. Ontologies address this challenge to meet specific data needs in the IoT field. This paper presents the implementation of a dynamic agriculture ontology-building tool that parses the ontology files to extract full data and update it based on the user needs. The technology is used to create the angular library for parsing the OWL files. The proposed ontology framework would accept user-defined ontologies and provide an interface for an online updating of the owl files to ensure the interoperability in the agriculture IoT.     

Interfacial microstructure and shear strength of Ag nano particle doped Sn-9Zn solder in ball grid array packages

Sn-9Zn solder joints containing Ag nano particles were prepared by mechanically mixing Ag nano particles (0.3, 0.5 and 1 wt%) with Sn-9Zn solder paste. In the monolithic Sn-Zn solder joints, scallop-shaped AuZn₃ intermetallic compound layers were found at their interfaces. However, after the addition of Ag nano particles, an additional uniform AgZn₃ intermetallic compound layer well adhered to the top surface of the AuZn₃ intermetallic compound layer was found. In addition, in the solder ball region, fine spherical-shaped AgZn₃ intermetallic compound particles were observed as well as Zn-rich and β-Sn phases. With the addition of Ag nano particles, the shear strengths consistently increased with an increase in the Ag nano particle content due to the uniform distribution of fine AgZn₃ intermetallic compound particles. The shear strength of monolithic Sn-Zn and 1 wt% Ag nano particle content Sn-Zn solder joints after one reflow cycle were about 42.1 MPa and 48.9 MPa, respectively, while their shear strengths after eight reflow cycles were about 39.0 MPa and 48.4 MPa, respectively. The AgZn₃ IMCs were found to be uniformly distributed in the β-Sn phase for Ag particle doped Sn-9Zn composite solder joints, which result in an increase in the tensile strength, due to a second phase dispersion strengthening mechanism. The fracture surface of monolithic Sn-Zn solder exhibited a brittle fracture mode with a smooth surface while Sn-Zn solder joints containing Ag nano particles showed a typical ductile failure with very rough dimpled surfaces.     

A statistical trust system in wireless mesh networks

Most trust and reputation solutions in wireless mesh networks (WMNs) rely on the intrusion detection system (IDS) Watchdog. Nevertheless, Watchdog does not consider packet loss on wireless links and may generate false positives. Consequently, a node that suffers from packet loss on one of its links may be accused wrongly, by Watchdog, of misbehaving. To deal with this issue, we propose in this paper a novel trust system which considers packet loss of links. Our trust system is based on a statistical detection method (SDM) implemented on each node of the network. Firstly, the SDM, via CUSUM test, analyzes the behavior of the packets loss in order to detect a dropping attack. Secondly, the SDM, through the Kolmogorov-Smirnov test, compares the behavior of the total packets loss with that of the control packets in order to identify the attack type. Our system allows every WMN’s node to assign to each of its neighbors, a trust value which reflects its real behavior. We have validated the proposed SDM method via extensive simulations on ns2 and have compared our trust system with an existing solution. The results display that our SDM solution offers better performance.     

Energy efficient scheduling in local area networks

Wireless Networks - In Wireless Local Area Networks (WLAN), portable devices such as notebooks, tabs, and smart phones are powered by batteries with limited energy. With the great increase of using...     

Performance evaluation and implementation complexity analysis framework for ZF based linear massive MIMO detection

Wireless Networks - This paper discusses a framework for algorithm-architecture synergy for (1) performance evaluation and (2) FPGA implementation complexity analysis of linear massive MIMO...     

CARD: A Contact-based Architecture for Resource Discovery in Wireless Ad Hoc Networks

Traditional protocols for routing in ad hoc networks attempt to obtain optimal or shortest paths, and in doing so may incur significant route discovery overhead. Such approaches may be appropriate for routing long-lived transfers where the initial cost of route discovery may be amortized over the life of the connection. For short-lived connections, however, such as resource discovery and small transfers, traditional shortest path approaches may be quite inefficient. In this paper we propose a novel architecture, CARD, for resource discovery in large-scale wireless ad hoc networks. Our mechanism is suitable for resource discovery as well as routing very small data transfers or transactions in which the cost of data transfer is much smaller than the cost of route discovery. Our architecture avoids expensive mechanisms such as global flooding and complex hierarchy formation and does not require any location information. In CARD resources within the vicinity of a node, up to a limited number of hops, are discovered using a proactive scheme. For resources beyond the vicinity, each node maintains a few distant nodes called contacts. Contacts help in creating a small world in the network and provide an efficient way to query for distant resources. Using contacts, the network view (or reachability) of the nodes increases, reducing the discovery overhead and increasing the success rate. On the other hand, increasing the number of contacts also increases control overhead. We study such trade-off in depth and present mechanisms for contact selection and maintenance that attempt to increase reachability with reduced overhead. Our schemes adapt gracefully to network dynamics and mobility using soft-state periodic mechanisms to validate and recover paths to contacts. Our simulation results show that CARD is scalable and can be configured to provide desirable performance for various network sizes. Comparisons with other schemes show overhead savings reaching over 93% (vs. flooding) and 80% (vs. bordercasting or zone routing) for high query rates in large-scale networks.     

CMOS RF switched capacitor bandpass filter tuned by ring VCO

A new RF switched capacitor bandpass filter and its command circuit made up of a ring voltage controlled oscillator with ‘XOR’ gates are proposed. Implemented in a standard CMOS technology, this circuit is intended to be used in a subset of professional mobile phone applications [380–520 MHz]. Experiments carried out on a prototype show a tunable center frequency range of 260 MHz [240–500 MHz], with a quality factor that can be as high as 300.