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81.
The orthogonal frequency-division multiplexing (OFDM) systems are highly sensitive to the nonlinear distortions introduced by the high-power amplifier at the transmitter and to the in-phase and quadrature (IQ) imbalance of the down converter at the receiver. In this paper, the joint effects of these impairments on the performance of the OFDM systems with M signal points quadrature amplitude modulation (M-QAM) are investigated. Moreover, the analytical formulations for the error vector magnitude, the bit error rate, and the total degradation performances of the M-QAM-OFDM systems in additive white Gaussian noise channels as a function of the output back off and IQ imbalance parameters are derived. The computer simulation results confirm the accuracy and validity of our proposed analytical approach. 相似文献
82.
Amir Seirafian Vahid Tabataba Vakily 《International Journal of Communication Systems》2009,22(2):203-217
Exact closed‐form expressions of the Cramer–Rao bound (CRB) for joint sampling clock offset and channel taps are obtained in multi‐carrier code division multiple access systems. CRB is undoubtedly the most well known variance's bound to determine. It provides a benchmark against which we can compare the performance of any unbiased estimator. Furthermore, minimum variance unbiased (MVU) estimator for these parameters is proposed. Moreover, maximum likelihood (ML) and least‐squares estimators for joint sampling clock offset and channel taps are presented. Best linear unbiased estimator is also introduced just for channel taps. The performances of the estimators are compared through simulation results with the proposed CRB. Our results show the better performances of MVU and ML estimators with more computational complexity compared with the others. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
83.
Mohammed Smadi Terence D. Todd Vytas Kezys Vahid Azhari Dongmei Zhao 《Wireless Networks》2008,14(6):815-829
In this paper we consider vertical handoff for enterprise-based dual-mode (DM) cellular/WLAN handsets. When the handset roams
out of WLAN coverage, the DM's cellular interface is used to maintain the call by anchoring it through an enterprise PSTN
gateway/PBX. Soft handoff can be achieved in this case if the gateway supports basic conference bridging, since a new leg
of the call can be established to the conference bridge while the existing media stream path is active. Unfortunately this
requires that all intra-enterprise calls be routed through the gateway when the call is established. In this paper we consider
a SIP based architecture to perform conferenced dual-mode handoff and propose a much more scalable mechanism for short-delay
environments, whereby active calls are handed off into the conference bridge prior to the initiation of the vertical handoff.
Results are presented which are taken from a dual-mode handset testbed, from analytic models, and from simulations which characterize
the scalability of the proposed mechanism.
Mohammed Smadi received the B.Eng and Mgmt and M.A.Sc degrees in Computer Engineering from McMaster University in Hamilton, Ontario, Canada.
Mohammed received an NSERC doctoral award in 2005 and is currently a Ph.D. student at the Wireless Networking Group at McMaster
University.
Terence D. Todd received the B.A.Sc, M.A.Sc and Ph.D. degrees in Electrical Engineering from the University of Waterloo, Waterloo, Ontario,
Canada. While at Waterloo he spent 3 years as a Research Associate with the Computer Communications Networks Group (CCNG).
He is currently a Professor of Electrical and Computer Engineering at McMaster University in Hamilton, Ontario, Canada.
Professor Todd spent 1991 on research leave in the Distributed Systems Research Department at AT&T Bell Laboratories in Murray
Hill, NJ. He also spent 1998 on research leave at The Olivetti and Oracle Research Laboratory in Cambridge, England. While
at ORL he worked on the piconet project which was an early embedded wireless network testbed.
Dr. Todd’s research interests include metropolitan/local area networks, wireless communications and the performance analysis
of computer communication networks and systems. He is a past Editor of the IEEE/ACM Transactions on Networking and currently
holds the NSERC/RIM/CITO Chair on Pico-Cellular Wireless Internet Access Networks.
Dr. Todd is a Professional Engineer in the province of Ontario and a member of the IEEE.
Vytas Kezys was born in Hamilton, Canada in 1957. He received the B.Eng. degree in Electrical Engineering from McMaster University, Canada,
in 1979.
From 1979 to 1998, Mr. Kezys was involved in radar and communications research as Principal Research Engineer at the Communications
Research Laboratory, McMaster University. While at McMaster, his research activities included array signal processing for
low-angle tracking radar, radar signal processing, and smart antennas for wireless communications. Mr. Kezys was founder and
President of TalariCom Inc., a start-up company that developed cost effective smart antenna technologies for broadband wireless
access applications.
Currently, Mr. Kezys is Director of Advanced Products at Research in Motion in Waterloo, Canada.
Vahid S. Azhari received his B.S. and M.S. from the Department of Electrical and Computer Engineering, IUST and University of Tehran, Iran,
in 2000 and 2003 respectively. His M.S. research focused on designing scheduling algorithms for switch fabrics. He also worked
for two years for the Iranian Telecommunication Research Centre on developing software for SDH switches. He is currently pursuing
his Ph.D. degree at the Wireless Networking Laboratory, McMaster University, Canada. His main area of research includes handoff
management in integrated wireless networks, WLAN deployment techniques, and wireless mesh networks.
Dongmei Zhao received the Ph.D. degree in Electrical and Computer Engineering from the University of Waterloo, Waterloo, Ontario, Canada
in June 2002. Since July 2002 she has been with the Department of Electrical and Computer Engineering, McMaster University,
Hamilton, Ontario, Canada where she is an assistant professor. Dr. Zhao’s research interests include modeling and performance
analysis, quality-of-service provisioning, access control and admission control in wireless cellular networks and integrated
cellular and ad hoc networks. Dr. Zhao is a member of the IEEE. 相似文献
84.
Shima Jafarzadeh Mehrdad Forough Vahid Javan Kouzegaran Masoumeh Zargar Farhad Garavand Maryam Azizi-Lalabadi Mehdi Abdollahi Seid Mahdi Jafari 《Comprehensive Reviews in Food Science and Food Safety》2023,22(4):2850-2886
Non-biodegradability and disposal problems are the major challenges associated with synthetic plastic packaging. This review article discusses a new generation of biodegradable active and smart packaging based on porous nanomaterials (PNMs), which maintains the quality and freshness of food products while meeting biodegradability requirements. PNMs have recently gained significant attention in the field of food packaging due to their large surface area, peculiar structures, functional flexibility, and thermal stability. We present for the first time the recently published literature on the incorporation of various PNMs into renewable materials to develop advanced, environmentally friendly, and high-quality packaging technology. Various emerging packaging technologies are discussed in this review, along with their advantages and disadvantages. Moreover, it provides general information about PNMs, their characterization, and fabrication methods. It also briefly describes the effects of different PNMs on the functionality of biopolymeric films. Furthermore, we examined how smart packaging loaded with PNMs can improve food shelf life and reduce food waste. The results indicate that PNMs play a critical role in improving the antimicrobial, thermal, physicochemical, and mechanical properties of natural packaging materials. These tailor-made materials can simultaneously extend the shelf life of food while reducing plastic usage and food waste. 相似文献
85.
Davoud Salarbashi Mohsen Tafaghodi Omid Rajabi Bibi Sedigheh Fazli Bazzaz Vahid Soheili 《Journal of Food Safety》2023,43(1):e13024
This study aimed to produce and characterize eco-friendly SSPS nanocomposites incorporated with various concentrations of TiO2 nanoparticles (NPs) (1%, 3%, and 7%). The antimicrobial activity of the nanocomposite films against five strains of pathogenic bacteria was examined. Salmonella typhi PTCC 1609 was the most sensitive species to TiO2 NPs at concentrations equal to the synthetic antibiotic. The migration of TiO2 to ethanol and acetic acid, as two food simulants increased when the initial nano-TiO2 content increased. The release profiles for TiO2 in two simulants of ethanol and acetic acid indicated a non-Fickian release, and the release kinetics were concentration-dependent. SSPS/TiO2 nanocomposites degraded easily and thus have the potential to be applied as an eco-friendly packaging system. Oral administration of doses of 1, 12.5, 25, 50, and 75 mg/kg TiO2 revealed that the dose of 50 and 75 mg/kg increased malondialdehyde (p < .001) concentration in the liver tissue. In addition, it decreased glutathione (p < .001) concentration in the liver tissue. 相似文献
86.
In this article, an analytical technique is introduced to obtain the excitation coefficients of uniformly spaced linear antenna arrays in order to achieve a desired array factor. By integration of the prescribed array factor, the array factor dependency to the progressive phase shift is eliminated. A new system of linear equations is consequently obtained whose solution represents the excitation coefficients of the array. Some examples are presented to verify the accuracy of the introduced method. The performance of this strategy is compared with those obtained by the other well‐known techniques such as Woodward‐Lawson and Fourier transform. It is shown that the presented method estimates the desired array pattern with a very good precision. 相似文献
87.
88.
89.
European Journal of Wood and Wood Products - In the current research work, moisture gradients and moisture induced stresses (MiS) were investigated in cross laminated timber (CLT) bearing... 相似文献
90.