1,721,064 research outputs found
Wideband active envelope load-pull for robust power amplifier and transistor characterisation
Get PDFThe advent of fourth generation (4G) wireless communication with available modulation bandwidth ranging from 1 MHz to 20 MHz is starting to emerge. The linear modulation technique being employed means that the power amplifiers that support the standards need to have high degree of linearity. By nature, however, all power amplifiers are non-linear. Load-pull measurement system provides anindispensable non-linear tool for the characterization of power amplifier and transistor for linearity enhancement. Conventional passive or active load-pull has delay problem that get worse as the modulation frequency is increased beyond few MHz. Furthermore in order to provide robust non-linear measurement, load-pull system needs to provide bandwidth at least five times the modulation bandwidth by including the fifth-order inter-modulation (IMD5). This thesis presents, for the first time, delay compensation on the unique active envelope load-pull architecture providing constant impedance for bandwidth up to 20 MHz. In doing so, it provides a superior load-pull measurement and also the ability to directly control in-band impedances. Artificial variations imposed on the in-band impedances offer further insight on power amplifier and transistor behaviours under wideband multi-tone stimulus.EThOS - Electronic Theses Online ServiceGBUnited Kingdo
Wideband active envelope load-pull for robust power amplifier and transistor characterisation
Get PDFThe advent of fourth generation (4G) wireless communication with available modulation bandwidth ranging from 1 MHz to 20 MHz is starting to emerge. The linear modulation technique being employed means that the power amplifiers that support the standards need to have high degree of linearity. By nature, however, all power amplifiers are non-linear. Load-pull measurement system provides anindispensable non-linear tool for the characterization of power amplifier and transistor for linearity enhancement. Conventional passive or active load-pull has delay problem that get worse as the modulation frequency is increased beyond few MHz. Furthermore in order to provide robust non-linear measurement, load-pull system needs to provide bandwidth at least five times the modulation bandwidth by including the fifth-order inter-modulation (IMD5). This thesis presents, for the first time, delay compensation on the unique active envelope load-pull architecture providing constant impedance for bandwidth up to 20 MHz. In doing so, it provides a superior load-pull measurement and also the ability to directly control in-band impedances. Artificial variations imposed on the in-band impedances offer further insight on power amplifier and transistor behaviours under wideband multi-tone stimulus
A low complexity peak-to-average power ratio reduction scheme using gray codes
Get PDFA low-complexity peak-to-average power ratio (PAPR) reduction scheme in an orthogonal frequency division multiplexing system is proposed. The proposed scheme utilizes a new phase sequence based on a gray code structure and a similarity measurement block. Due to the ordered phase sequences, a noteworthy reduction capacity is obtained in terms of the number of multiplication and addition operations and the side information. Simulations are performed with quadrature phase shift keying modulation and a Saleh model power amplifier. The proposed scheme offers a significant PAPR reduction and bit error rate performance at approximately the same total complexity compared to the conventional partial transmit sequence and the enhanced partial transmit sequence (EPTS) techniques. The results show that at the same PAPR reduction, this scheme provides a complexity reduction of at least 42.3 % over that of the EPTS technique
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
A survey of state of the art: hierarchical routing algorithms for wireless sensor networks
Get PDFGenerally, any device that has the ability to sense the surrounding environment can be considered as a sensor node. A wireless sensor network is a group of sensor nodes that cooperate with each other, it may contain a few numbers of sensors or it can consist of thousands of sensors. Wireless sensor networks can be used in wide range of applications such as measuring temperature, humidity, pressure, noise level, monitoring the vehicular movement, military applications and health applications. One of the main crucial issues can face the operation and the surveillance of wireless sensor networks is energy consumption. Energy in wireless sensor networks mostly powered by battery and the greatest share of this energy is consumed during data transmission. Many researches have been done to solve this problem or at least find a solution to decrease the energy consumption. One of those solutions is using efficient routing algorithm. The most efficient type of algorithms that can be used for WSNs in large areas is hierarchical routing algorithms. In this article, we will present a review for the state of the art for recent hierarchical algorithms. Moreover, we will use criteria to classify the hierarchical algorithms that never used before in any article, which is the mechanism that implemented in the hierarchical algorithm such as clustering, chaining, or hybrid between cluster and chain
Fast and secure handover authentication scheme in Mobile WiMax
Get PDFHandover is one of the essential elements that can affect the Quality of Service (QoS) and capacity of Mobile Broadband Networks. The next generation of broadband wireless networks including the IEEE802.16e standard, allow users to roam seamlessly and securely over the network. Unfortunately the current design suffers from lengthy delay between breaking of previous connection and making of next connection. This delay might not be tolerated by some of the real-time applications such as VoIP and video streaming. Therefore the need for fast and secure handover design becomes an urging necessity. This paper proposes a new handover mechanism enables fast and secure handover with minimum delay suitable for real-time applications. It should be pointed that this proposed handover protocol guarantees a forward and backward secrecy. We conducted our research using ns-2 simulation tool
Energy efficient Two Stage Chain Routing Protocol (TSCP) for wireless sensor networks
Get PDFWireless sensor nodes are mostly used in extreme environments, especially at remote and hostile areas including battlefield, volcanoes and underwater. Thus, it is difficult to replenish the energy source of the sensor node once it is installed. In order to prolong the lifetime of the nodes, we propose a new routing algorithm that can achieve significant energy conservation in WSNs, known as Two Stage Chain Routing Protocol (TSCP). The main objectives of TSCP is to minimize the total energy consumption, achieve more load balancing and increase the network lifetime with more stability compared with other routing algorithms, for examples Chain-Cluster based Mixed routing (CCM) and Chain-Chain Based Routing Protocol (CCBRP). TSCP algorithm divides the sensor network into multiple chains and work within two stages. The first stage is dividing the nodes to horizontal chains that include all sensor nodes within the same row and the second stage is forming a vertical chain that includes all chain heads. The mechanism for selecting the heads in each row is sequentially chosen with all the heads belong to the same column. In the second stage, the node with maximum residual energy amongst the chain heads will be the main head that functions as a gateway to the base station. Simulation results show that TSCP outperforms CCM and CCBRP in overall energy conservation, network lifetime and stability
RF CMOS switch design methodologies for multiband transceiver applications
Get PDFMultimode multiband connectivity has become a de-facto requirement for smartphones with 3G WCDMA/4G LTE applications. In transceivers, multiband operation is achieved by selecting an output from two or more signal path targeting for a specific frequency range in parallel or by using switched capacitor/inductor. In this paper, design methodology of 280nm CMOS switch is presented. Design optimization of RF CMOS switch is presented which is deciding proper selection of CMOS transistor parameters and switch size as per external circuit parameters. The CMOS switch of a 5-transistor stack with W/L=1200µm/280nm provides insertion loss 14dB. The switches designed when implemented in a multiband power amplifier (PA) exhibits 36dB gain at 1900MHz high-band and 34.5dB gain at 900MHz low-band with 27.5dBm peak power at both bands. The switch design methodologies presented in this paper should be of use in designing various blocks in emerging multiband transceiver applications
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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