Home About us Contact
|
Home About us Contact | ||
|
|
||
Phase Modulation (phase + modulation)
Selected AbstractsPerformance of duo-stage SOA based all-optical multicasting switching matrix for future grid networkingMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 1 2007Bernard H. L. Lee Abstract This paper presents the performance evaluation of a duo-stage SOA based All-Optical Multicasting capable Switch architecture suitable for the requirements of Grid Networking. SOAs based devices are located at the input and the output ports of the switch. The SOAs located at the input port serves as a multicasting and routing device feeding the signals into an N × N arrayed waveguide gratings and the SOAs at the output are regenerators to restore the quality of the signals before sending them into the network. This design uses the non-linearity processes in SOA such as Cross Gain Modulation and Cross Phase Modulation to achieve a maximum of 1,16 multicast at a bit-rate of 10 Gbps within the all-optical switch. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 59,62, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22031 [source] The theory of cosy NMR experiments revisited: Application to an AX spin system of quadrupolar nucleiCONCEPTS IN MAGNETIC RESONANCE, Issue 3 2010P. Kempgens Abstract The two-dimensional nuclear magnetic resonance correlation spectroscopy (2D NMR COSY) spectrum of an AX spin system of spin-1 has been calculated by numerical density matrix calculations. The mathematical expressions found are valid for an AX spin system of any spins. These expressions should be used to calculate the 2D NMR COSY spectrum of an AX spin system of high spin nuclei as their use will significantly simplify the calculations. More precisely, one needs to calculate only one set of coefficients despite the need of two steps in the phase cycling to achieve phase modulation during t1. © 2010 Wiley Periodicals, Inc. Concepts Magn Reson Part A 36A: 170,177, 2010. [source] Intermediate frequency zero-crossing detection of filtered MSK based on irregular samplingEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 7 2007Tobias Scholand Short range communication systems such as Bluetooth and DECT (Digital Enhanced Cordless Telecommunications) deploy Gaussian frequency shift keying (GFSK), which is a continuous phase modulation (CPM) scheme derived from minimum shift keying (MSK). Since these short range communication systems require low-cost transceiver structures, the development of appropriate receiver techniques has been a major research topic. Particularly, analogue limiter--discriminator--integrator (LDI) dump filtering techniques have received considerable attention. With the availability of digital signal processing (DSP), the digital implementation of LDI techniques has become increasingly attractive. In order to make LDI receivers more accessible, zero-crossing detection was proposed. First, the authors shall focus on the establishment of an appropriate mathematical discrete-time system model, taking bandlimiting receiver filters into account explicitly. This system model serves as the basis for the development of a multitude of digital zero-crossing detection techniques. Starting from this mathematical discrete-time system model, the authors shall focus on a novel, yet promising, approach to digital zero-crossing detection in the intermediate frequency domain, using irregular sampling instead of the commonly employed regular sampling. The novel detectors shall be termed zero-crossing decorrelation detectors (ZXDDs), because a decorrelating approach will be used. The authors shall present three different variants of the ZXDD. The performance of these ZXDD schemes has been analysed in simulations by the authors and obtained results shall be presented and compared to the performance of known LDI and zero-crossing detection based techniques. Copyright © 2007 John Wiley & Sons, Ltd. [source] Serially concatenated continuous phase modulation with symbol interleavers: performance, properties and design principlesEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 4 2006Ming Xiao Serially concatenated continuous phase modulation (SCCPM) systems with symbol interleavers are investigated. The transmitted signals are disturbed by additive white Gaussian noise (AWGN). Compared to bit interleaved SCCPM systems, this scheme shows a substantial improvement in the convergence threshold at the price of a higher error floor. In addition to showing this property, we also investigate the underlying reason by error event analysis. In order to estimate bit error rate (BER) performance, we generalise traditional union bounds for a bit interleaver to this non-binary interleaver. For the latter, both the order and the position of permuted non-zero symbols have to be considered. From the analysis, some principal properties are identified. Finally, some design principles are proposed. Our paper concentrates on SCCPM, but the proposed analysis methods and conclusions can be widely used in many other systems such as serially concatenated trellis coded modulation (SCTCM) et cetera. Copyright © 2006 AEIT [source] Trellis coded quantization/trellis coded continuous phase modulation over Rician channel with imperfect phase referenceEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 5 2004Osman Nuri Ucan In this paper, to improve bandwidth efficiency and error performance, trellis coded quantization/trellis continuous phase modulation (TCQ/TCPM) are combined and a trellis coded quantization/trellis coded continuous phase modulation (TCQ/TCCPM) scheme is introduced. Here, we use TCQ/TCM system as source coding because of its advantage over classical joint systems in terms of decoding time and complexity. We also present CPM for TCQ/TCM signals, since CPM provides low spectral occupancy and is suitable for power and bandwidth limited channels. The bit error performance of TCQ/TCCPM schemes is derived taking into account quantization noise over Rician channel with imperfect phase reference. The analytical upper bounds are obtained using Chernoff bounding technique, combined with the modified generating functional approach with no channel state information (CSI) and no side information for the phase noise process. As an example, TCQ/TCCPM scheme for 16CPFSK with modulation index h,=,1/2 (16CPFSK-TCQ/TCCPM) is investigated and compared to TCQ/TCM for 16PSK (16PSK-TCQ/TCM). It is shown that 16CPFSK-TCQ/TCCPM has better bit error performance than 16PSK-TCQ/TCM in all signal-to-noise-ratio (SNR) and quantization noise effect increases at high SNR values for both uniform and optimum quantization. Copyright © 2004 AEI. [source] Blind equalization of space-time-turbo trellis coded/continuous phase modulation over Rician fading channelsEUROPEAN TRANSACTIONS ON TELECOMMUNICATIONS, Issue 5 2004Osman N. Ucan In this paper, to improve bit error performance and bandwidth efficiency, we combine space-time block codes (STBC), turbo trellis codes and continuous phase modulation and denote space-time-turbo trellis coded/continuous phase modulation (ST-TTC/CPM). For high data transmission over wireless fading channels, STBC provide the maximal possible diversity advantage for multiple decoding algorithms. We present continuous phase modulation (CPM) for ST-TTC signals, since CPM provides low-spectral occupancy and is suitable for power and bandwidth-limited channels. In our model, to utilize STBC efficiently, we need to estimate the channel parameters, which influence the signals having continuity property. Therefore, we develop a blind maximum likelihood channel estimation algorithm for signals propagating through a Rician fading channel. Here, Baum-Welch (BW) algorithm, based on hidden Markov model (HMM), is modified to provide computationally efficient channel parameter estimation. We also investigate the performance of ST-TTC/CPM in the case of no channel state information (CSI) for various Rician parameters K and Doppler frequency. Copyright © 2004 AEI. [source] The Mammalian Circadian Clock Exhibits Acute Tolerance to EthanolALCOHOLISM, Issue 12 2009Rebecca A. Prosser Background:, Tolerance to ethanol is observed over a variety of time courses, from minutes to days. Acute tolerance, which develops over 5 to 60 minutes, has been observed for both behavioral and neurophysiological variables and may involve changes in signaling through NMDA, GABA, or other receptors. Previous work has shown that both acute and chronic ethanol treatments modulate photic and nonphotic phase resetting of the mammalian circadian clock located in the suprachiasmatic nucleus (SCN). Although not specifically tested, the data thus far do not point to the development of chronic tolerance to the modulatory effects of ethanol. Here we investigated whether acute tolerance the ethanol occurs with respect to in vitro phase modulation of the SCN clock. Methods:, Mouse brain slices containing the SCN were pretreated with ethanol for varying lengths of time, followed by treatment concurrent with either glutamate or the serotonin agonist, 8-hydroxy-DPAT (DPAT). The phase of the SCN circadian clock was assessed the following day through extracellular recordings of SCN neuronal activity. SCN neuronal activity normally peaks during mid-day, and this rhythm can be shifted by treatment with either glutamate or DPAT. Results:, While concurrent treatment of SCN-containing brain slices with ethanol and glutamate blocks glutamate-induced phase delays of the SCN clock, pretreating the slices with ethanol for ,15 minutes prevents this inhibition. Likewise, while concurrent treatment with ethanol and DPAT enhances DPAT-induced phase advances of the SCN clock, pretreating the slices with ethanol for ,30 minutes prevents this enhancement. Conclusions:, Both the inhibiting and enhancing effects of ethanol on in vitro SCN clock phase resetting show acute tolerance. Additional experiments are needed to determine whether more slowly developing forms of tolerance also occur with respect to the SCN circadian clock. [source] Efficient low-power heteronuclear decoupling in 13C high-resolution solid-state NMR under fast magic angle spinningMAGNETIC RESONANCE IN CHEMISTRY, Issue S1 2007Mrignayani Kotecha Abstract The use of a low-power two-pulse phase modulation (TPPM) sequence is proposed for efficient 1H radio frequency (rf) decoupling in high-resolution 13C solid-state NMR (SSNMR) under fast MAS conditions. Decoupling efficiency for different low-power decoupling sequences such as continuous-wave (cw), TPPM, XiX, and ,-pulse (PIPS) train decoupling has been investigated at a spinning speed of 40 kHz for 13C CPMAS spectra of uniformly 13C - and 15N -labeled L -alanine. It was found that the TPPM decoupling sequence, which was originally designed for high-power decoupling, provides the best decoupling efficiency at low power among all the low-power decoupling sequences examined here. Optimum performance of the low-power TPPM sequence was found to be obtained at a decoupling field intensity (,1) of ,,R/4 with a pulse flip angle of ,, and a phase alternation between ± ,(, = ,20° ), where ,R/2, is the spinning speed. The sensitivity obtained for 13CO2,, 13CH, and 13CH3 in L -alanine under low-power TPPM at ,1/2, of 10 kHz was only 5,15% less than that under high-power TPPM at ,1/2, of 200 kHz, despite the fact that only 0.25% of the rf power was required in low-power TPPM. Analysis of the 13CH2 signals for uniformly 13C- and 15N-labeled L -isoleucine under various low-power decoupling sequences also confirmed superior performance of the low-power TPPM sequence, although the intensity obtained by low-power TPPM was 61% of that obtained by high-power TPPM. 13C CPMAS spectra of 13C -labeled ubiquitin micro crystals obtained by low-power TPPM demonstrates that the low-power TPPM sequence is a practical option that provides excellent resolution and sensitivity in 13C SSNMR for hydrated proteins. Copyright © 2007 John Wiley & Sons, Ltd. [source] A simple approach for phase-modulated single-scan 2D NMR spectroscopyMAGNETIC RESONANCE IN CHEMISTRY, Issue 10 2005Nikolas Salisbury Andersen Abstract Conventional NMR spectroscopy techniques require long acquisition times due to the recovery time between the repeated excitations necessary for each increment of the evolution times in the indirectly detected dimensions. Here we outline a pulse sequence element for gradient-assisted ultrafast multidimensional NMR spectroscopy using frequency-modulated ,chirp' pulses to generate phase-modulated magnetization in an indirectly detected spectral dimension. The potential of this sequence element is demonstrated by acquiring a correlation spectroscopy (COSY) spectrum in 96 ms. This new pulse sequence element is an extension of ultrafast spectroscopy techniques based on the generation of amplitude modulation of the NMR signal in the indirectly detected spectral dimensions. The use of phase modulation instead of amplitude modulation helps broaden the applicability and may provide an increase of sensitivity in some experiments due to the ability to distinguish between positive and negative frequency offsets relative to the carrier frequency of the sequence element. Copyright © 2005 John Wiley & Sons, Ltd. [source] On the application of a non-CPMG single-shot fast spin-echo sequence to diffusion tensor MRI of the human brainMAGNETIC RESONANCE IN MEDICINE, Issue 1 2002Mark E. Bastin Abstract The strong sensitivity of Carr-Purcell-Meiboom-Gill (CPMG) fast spin-echo (FSE) sequences, such as rapid acquisition with relaxation enhancement (RARE), to the phase of the prepared transverse magnetization means that artifact-free single-shot diffusion-weighted images can currently only be obtained with a 30,50% reduction in the signal-to-noise ratio (SNR). However, this phase sensitivity and signal loss can be addressed in FSE sequences that use quadratic phase modulation of the radiofrequency (RF) refocusing pulses to generate a sustained train of stable echoes. Here the first application of such a non-CPMG single-shot FSE (ssFSE) sequence to diffusion tensor MR imaging (DT-MRI) of the human brain is described. This approach provides high SNR diffusion-weighted images that have little or no susceptibility to poor B0 magnetic field homogeneity and the strong eddy currents typically present in DT-MRI experiments. Magn Reson Med 48:6,14, 2002. © 2002 Wiley-Liss, Inc. [source] Optical mm-wave generation based on phase modulation along with optical filteringMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 8 2007Jianxin Ma Abstract We have investigated the generation and transmission of optical millimeter (mm)-wave signal based on optical phase modulator (PM) and fiber Bragg grating (FBG) filter. With an optimized modulation depth of PM and a higher carrier suppression ratio via a notch filter, the generated optical mm-wave can be transmitted over a long-distance without fading. We have also theoretically analyzed the impact of time shift on the eye closure of optical and electrical signal due to the fiber dispersion, which is well in accord with the experimental results. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1787,1793, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22622 [source] Phase modulation effects in X-ray diffraction from a highly deformed crystal with variable strain gradientACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2009M. Shevchenko The X-ray interbranch scattering by lattice distortions is studied for a thin crystal whose thickness is appreciably less than the conventional X-ray extinction length. The concept of interbranch phase modulation of the X-ray wavefield is extended to the case of a large gradient which depends on depth inside the crystal. The prominent interbranch features of the diffracted intensity are also established within this concept. Numerical calculations of the diffracted intensity are presented for an exponential strain gradient model to illustrate this. Diffraction (extinction) contrast is discussed for a strongly deformed specimen containing a single dislocation. It is predicted that for large values of the X-ray extinction length the extinction contrast may arise even in the case of a very thin crystal. This effect, owing to the interbranch phase changes of the waves scattered in the deformed matrix, is observed in experiments with protein crystals. [source] Cytogenetic damage in human lymphocytes following GMSK phase modulated microwave exposureBIOELECTROMAGNETICS, Issue 1 2002Guglielmo d'Ambrosio Abstract The present study investigated, using in vitro experiments on human lymphocytes, whether exposure to a microwave frequency used for mobile communication, either unmodulated or in presence of phase only modulation, can cause modification of cell proliferation kinetics and/or genotoxic effects, by evaluating the cytokinesis block proliferation index and the micronucleus frequency. In the GSM 1800 mobile communication systems the field is both phase (Gaussian minimum shift keying, GMSK) and amplitude (time domain multiple access, TDMA) modulated. The present study investigated only the effects of phase modulation, and no amplitude modulation was applied. Human peripheral blood cultures were exposed to 1.748 GHz, either continuous wave (CW) or phase only modulated wave (GMSK), for 15 min. The maximum specific absorption rate (,5 W/kg) was higher than that occurring in the head of mobile phone users; however, no changes were found in cell proliferation kinetics after exposure to either CW or GMSK fields. As far as genotoxicity is concerned, the micronucleus frequency result was not affected by CW exposure; however, a statistically significant micronucleus effect was found following exposure to phase modulated field. These results would suggest a genotoxic power of the phase modulation per se. Bioelectromagnetics 23:7,13, 2002. © 2002 Wiley-Liss, Inc. [source] Quantitative phase microscopy: A new tool for investigating the structure and function of unstained live cellsCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 12 2004Claire L Curl SUMMARY 1.,The optical transparency of unstained live cell specimens limits the extent to which information can be recovered from bright-field microscopic images because these specimens generally lack visible amplitude-modulating components. However, visualization of the phase modulation that occurs when light traverses these specimens can provide additional information. 2.,Optical phase microscopy and derivatives of this technique, such as differential interference contrast (DIC) and Hoffman modulation contrast (HMC), have been used widely in the study of cellular materials. With these techniques, enhanced contrast is achieved, which is useful in viewing specimens, but does not allow quantitative information to be extracted from the phase content available in the images. 3.,An innovative computational approach to phase microscopy, which provides mathematically derived information about specimen phase-modulating characteristics, has been described recently. Known as quantitative phase microscopy (QPM), this method derives quantitative phase measurements from images captured using a bright-field microscope without phase- or interference-contrast optics. 4.,The phase map generated from the bright-field images by the QPM method can be used to emulate other contrast image modes (including DIC and HMC) for qualitative viewing. Quantitative phase microscopy achieves improved discrimination of cellular detail, which permits more rigorous image analysis procedures to be undertaken compared with conventional optical methods. 5.,The phase map contains information about cell thickness and refractive index and can allow quantification of cellular morphology under experimental conditions. As an example, the proliferative properties of smooth muscle cells have been evaluated using QPM to track growth and confluency of cell cultures. Quantitative phase microscopy has also been used to investigate erythrocyte cell volume and morphology in different osmotic environments. 6.,Quantitative phase microscopy is a valuable, new, non-destructive, non-interventional experimental tool for structural and functional cellular investigations. [source] | ||||||||||||||||