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Wireless Communication Systems (wireless + communication_system)

Distribution by Scientific Domains

Engineering	75%

Selected Abstracts

A utility-based capacity optimization framework for achieving cooperative diversity in the hierarchical converged heterogeneous wireless networks

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 12 2008
Mugen Peng
Abstract A hierarchical convergence mechanism for the heterogeneous wireless communication system via the heterogeneous cooperative relay node is presented in this paper, in which the techniques of cooperative communication and wireless relay are utilized to improve performances of the individual user and the overall converged networks. In order to evaluate the benefits of the proposal, a utility-based capacity optimization framework for achieving the heterogeneous cooperative diversity gain is proposed. The heterogeneous cooperative capacity, relay selection and power allocation theoretical models are derived individually. The joint optimization model for relay selection and power allocation is presented as well. Owing to the computation complexity, the sub-optimal cooperative relay selection algorithm, the sub-optimal power allocation algorithm and the sub-optimal joint algorithm are determined to approach the maximum overall networks' spectrum efficiency. These proposed algorithms are designed in conformance to guarantee the equivalent transmission rates of the different wireless access networks. The simulation results demonstrate that the utility-based capacity model is available for the heterogeneous cooperative wireless communication system, and the proposed algorithms can improve performances by achieving the cooperative gain and taking full advantage of the cross-layer design. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Parallel combinatory multiple-subcarrier optical wireless communication systems

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 3 2005
Norio Kitamoto
Abstract We analyse the performance of parallel combinatory multiple-subcarrier (PC-MS) optical wireless communication system. The PC-MS system can transmit more information at each symbol interval than conventional MS systems with the same subcarriers. In addition the PC-MS system can decrease the bias that must be added to the MS electrical signal, because the number of subcarriers other than null subcarriers is smaller than that in the conventional MS systems and thus the minimum power becomes larger. Therefore, the PC-MS system can decrease the required energy per bit. Copyright © 2005 John Wiley & Sons, Ltd. [source]

An integrated packaging antenna-diplexer module for cellular/SDMB bands with LTCC technology

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 4 2009
Jeung Uk Ha
Abstract This article presents an integrated packaging antenna-diplexer module for wireless communication system in the cellular and satellite digital multimedia broadcasting (SDMB) band. Multilayer low temperature cofired ceramic (LTCC) technology with integration capability was used in design and fabrication of the proposed module. To achieve a compact integration, an inverted-F antenna (IFA) with a meander line and a diplexer composed of low-pass filter (LPF) and high-pass filter (HPF) was embedded. The proposed module with dimension of 27.5 × 12.0 × 2.2 mm3 operates over a range from 813 to 902 MHz for the cellular band and from 2586 to 2655 MHz for the SDMB band. An isolation level below ,25 dB was obtained at each band. The measured gains of the fabricated module are ,1.96 and ,5.43 dBi, respectively. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1039,1043, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24244 [source]

Exploiting the short,term and long,term channel properties in space and time: Eigenbeamforming concepts for the BS in WCDMA

EUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 5 2001
Christopher Brunner
The deployment of adaptive antennas at base stations considerably increases the spectral efficiency of wireless communication systems. To reduce the computational complexity and increase performance of space,time (ST) processing, processing may take place in reduced dimension, i. e., pre,filtering takes place which is related to linear estimation theory based on second order statistics. To this end, long,term and short,term channel estimates are integrated into specific Tx/Rx systems. In this article, we present a new ST rake structure for uplink reception in WCDMA which operates in reduced dimension. Accordingly, our approach combines short,term and long,term spatial and temporal channel properties using an eigenanalysis. By choosing dominant eigenbeams in time and space, the algorithm enhances interference suppression as well as spatial and temporal receive diversity. In contrast to previously introduced well,known receiver structures, the ST eigenrake inherently adapts to different propagation environments and achieves higher spectral efficiency than other receivers. This is illustrated by Monte,Carlo simulations. Then we extend the proposed concept to the downlink. The downlink eigenbeamformer improves closed,loop downlink diversity compared to other proposals in standardization (3GPP) which only exploit short,term channel properties. Even though the short,term feedback rate remains unchanged, additional antenna elements can be included to increase antenna and diversity gain. We also present a tracking solution to the downlink eigenbeamforming in WCDMA. To this end, we propose a distributed implementation of the eigenspace/,beam tracking at the mobile terminal and base station (BS), respectively. Moreover, the specific nature of the deployed tracking scheme offers an advantageous feedback signalling. [source]

Adaptive pattern nulling design of linear array antenna by phase-only perturbations using memetic algorithms

INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING, Issue 11 2008
Chao-Hsing Hsu
Abstract In this paper, the pattern nulling of a linear array for interference cancellation is derived by phase-only perturbations using memetic algorithms (MAs). The MAs uses improvement procedures which is obtained by incorporating local search into the genetic algorithms. It is proposed to improve the search ability of genetic algorithms. MA is a kind of an improved type of the traditional genetic algorithms. By using local search procedure, it can avoid the shortcoming of the traditional genetic algorithms, whose termination criteria are set up by using the trial and error method. The MA is applied to find the pattern nulling of the proposed adaptive antenna. This design for radiation pattern nulling of an adaptive antenna can suppress interference by placing a null at the direction of the interfering source, i.e. to increase the signal to interference ratio. This proposed method is that an innovative adaptive antenna optimization technique is also able to solve the multipath problem which exists in practical wireless communication systems. Two examples are provided to justify the proposed phase-only perturbations approach based on MAs. Computer simulation results are given to demonstrate the effectiveness of the proposed method. Copyright © 2007 John Wiley & Sons, Ltd. [source]

Parallel combinatory multiple-subcarrier optical wireless communication systems

Multiple spot diffusing geometries for indoor optical wireless communication systems

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 10 2003
A. G. Al-Ghamdi
Abstract In order to improve the performance of indoor optical wireless communication links, two multispot diffusing geometries based on diamond and line strip spot distribution geometries are proposed, analysed and compared to the known uniform spot distribution. Such geometries combine the advantages of the diffuse and the line-of-sight systems, giving great robustness and ease of use. The novel line strip multibeam transmitter geometry has resulted in a receiver signal-to-noise ratio (SNR) improvement of about 4 dB compared to the conventional diffuse system as well as a significant reduction in the pulse spread. Simulation and comparison results for both the conventional diffuse system and the three multispot diffusing geometries are presented. Further, pulse responses, SNR, and delay spread results at various locations are presented. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Experimental studies of direction of arrivals using a smart antenna testbed in wireless communication systems

INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS, Issue 3 2003
Shiann-Shiun Jeng
Abstract This paper presents some preliminary results from experimental studies on space-division-multiple-access (SDMA) for wireless communications. A smart antenna system utilizing direction-of-arrival (DOA)-based beamforming techniques can enhance signal quality by reducing co-channel interference from mobiles located at angles spatially distinct from the base station. Adopting both smart uplink and downlink beamforming, a communication system with an antenna array can increase the cell coverage of a base station and significantly boost capacity compared with conventional antenna systems. However, successful implementation of DOA-based beamforming techniques depends on the DOA characteristics. This paper presented the feasibility of direction finding and DOA variation with respect to frequency. Furthermore, the angle spread was studied for selected environments. The results demonstrate the feasibility of applying proposed smart antenna system utilizing DOA-based beamforming algorithm for increasing channel capacity and improving system performance in frequency-division-duplex (FDD) wireless communication systems. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Compact multiband slotted antenna for wireless communication applications

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 2 2009
Yi-Chieh Lee
Abstract New design of a compact antenna with slotted structure for multioperating bands of wireless communication systems is presented. By using compact configuration and slot designs on printed circuit board, the proposed antenna has the multiband measured operations for covering the 2.4-GHz WLAN (2.4,2.484 GHz), the WiMAX (IEEE 802.16e in the Taiwan: 2.5,2.69/3.5,3.65 GHz), and the 5-GHz WLAN (5.15,5.35/5.725,5.825 GHz) bands. Several properties of the proposed compact antenna for multiband operation such as impedance bandwidth, radiation pattern, and measured gain have been numerically and experimentally investigated. © 2008 Wiley Periodcals, Inc. Microwave Opt Technol Lett 51: 502,503, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24094 [source]

Switchless bidirectional amplifier for wireless communication systems

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 8 2007
A. Sevinc Aydinlik Bechteler
Abstract A bidirectional amplifier working at 2.4 GHz is presented in this article. The presented amplifier is able to amplify two signals simultaneously. This, since commonly used radio frequency switches are replaced by circulators. The amplifier is designed on a single small-sized printed circuit board. First, the new amplifier circuit is proposed and characterized. Then, its advantages and design problems are analyzed. Finally, design instructions are setup in order to obtain a good performance of the switchless amplifier within the frequency band of interest. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1888,1890, 2007; Published online in Wiley Inter-Science (www.interscience.wiley.com). DOI 10.1002/mop.22631 [source]

Microstrip antennas for cellular and wireless communication systems

MICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 5 2002
obodzian
Abstract The Letter describes problems related to use of microstrip antennas in cellular and wireless telecommunications systems. Because of the unique properties, microstrip technology is nowadays often used to manufacture small internal antennas for portable terminals as well as antenna arrays for base stations. It also seems to be a very promising technology for multisystem antennas, for which there is an ever-growing demand. The Letter also presents a short overview of currently available solutions and ones under development by the authors, along with some key problems related to their design. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 34: 380,384, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10468 [source]

Signal-to-interference-plus-noise ratio estimation for wireless communication systems: Methods and analysis

NAVAL RESEARCH LOGISTICS: AN INTERNATIONAL JOURNAL, Issue 5 2004
Daniel R. Jeske
Abstract The Signal-to-Interference-plus-Noise Ratio (SINR) is an important metric of wireless communication link quality. SINR estimates have several important applications. These include optimizing the transmit power level for a target quality of service, assisting with handoff decisions and dynamically adapting the data rate for wireless Internet applications. Accurate SINR estimation provides for both a more efficient system and a higher user-perceived quality of service. In this paper, we develop new SINR estimators and compare their mean squared error (MSE) performance. We show that our new estimators dominate estimators that have previously appeared in the literature with respect to MSE. The sequence of transmitted bits in wireless communication systems consists of both pilot bits (which are known both to the transmitter and receiver) and user bits (which are known only by the transmitter). The SINR estimators we consider alternatively depend exclusively on pilot bits, exclusively on user bits, or simultaneously use both pilot and user bits. In addition, we consider estimators that utilize smoothing and feedback mechanisms. Smoothed estimators are motivated by the fact that the interference component of the SINR changes relatively slowly with time, typically with the addition or departure of a user to the system. Feedback estimators are motivated by the fact that receivers typically decode bits correctly with a very high probability, and therefore user bits can be thought of as quasipilot bits. For each estimator discussed, we derive an exact or approximate formula for its MSE. Satterthwaite approximations, noncentral F distributions (singly and doubly) and distribution theory of quadratic forms are the key statistical tools used in developing the MSE formulas. In the case of approximate MSE formulas, we validate their accuracy using simulation techniques. The approximate MSE formulas, of interest in their own right for comparing the quality of the estimators, are also used for optimally combining estimators. In particular, we derive optimal weights for linearly combining an estimator based on pilot bits with an estimator based on user bits. The optimal weights depend on the MSE of the two estimators being combined, and thus the accurate approximate MSE formulas can conveniently be used. The optimal weights also depend on the unknown SINR, and therefore need to be estimated in order to construct a useable combined estimator. The impact on the MSE of the combined estimator due to estimating the weights is examined. © 2004 Wiley Periodicals, Inc. Naval Research Logistics, 2004 [source]

Power variations of wireless communication systems

BIOELECTROMAGNETICS, Issue 4 2010
J.B. Andersen
Abstract The use of wireless digital communication devices like GSM, WCDMA, HSPA, DECT, and WiFi changes the exposure of electromagnetic waves toward the user. Concentrating on the power variations on a slow and fast time scale, these new systems are discussed. Experimental results for both uplink and downlink are included for a sample of systems. The spectrum of the power fluctuations is seen as a convenient and compact way of describing very complex system behavior. The results are of interest for scientific studies of epidemiology and biological effects, and for general electromagnetic compatibility (EMC) aspects. Bioelectromagnetics 31:302,310, 2010. © 2010 Wiley-Liss, Inc. [source]

Low-power millimeter wave radiations do not alter stress-sensitive gene expression of chaperone proteins

BIOELECTROMAGNETICS, Issue 3 2007
M. Zhadobov
Abstract This article reports experimental results on the influence of low-power millimeter wave (MMW) radiation at 60 GHz on a set of stress-sensitive gene expression of molecular chaperones, namely clusterin (CLU) and HSP70, in a human brain cell line. Selection of the exposure frequency is determined by its near-future applications for the new broadband civil wireless communication systems including wireless local area networks (WLAN) for domestic and professional uses. Frequencies around 60 GHz are strongly attenuated in the earth's atmosphere and such radiations represent a new environmental factor. An exposure system operating in V-band (50,75 GHz) was developed for cell exposure. U-251 MG glial cell line was sham-exposed or exposed to MMW radiation for different durations (1,33 h) and two different power densities (5.4 µW/cm2 or 0.54 mW/cm2). As gene expression is a multiple-step process, we analyzed chaperone proteins induction at different levels. First, using luciferase reporter gene, we investigated potential effect of MMWs on the activation of transcription factors (TFs) and gene promoter activity. Next, using RT-PCR and Western blot assays, we verified whether MMW exposure could alter RNA accumulation, translation, or protein stability. Experimental data demonstrated the absence of significant modifications in gene transcription, mRNA, and protein amount for the considered stress-sensitive genes for the exposure durations and power densities investigated. The main results of this study suggest that low-power 60 GHz radiation does not modify stress-sensitive gene expression of chaperone proteins. Bioelectromagnetics 28:188,196, 2007. © 2006 Wiley-Liss, Inc. [source]