Opto-electronic modulation spectroscopy (OEMS)

A technique is described which combines wavelength modulated monochromatic illumination with impedance measurements to discriminate the responses of bulk and surface states in the depletion regions of electronic devices. The method reveals the inherent ambiguity in conventional capacitance vs voltage and conductance vs voltage (C-V and G-V) measurements of state densities. The opto-electronic modulation spectroscopy (OEMS) spectra peak energies provide the state to band transition energies directly and these can be indexed onto an energy diagram to give the spatial positions of the responding states as well as the band with which they communicate. Measurements made on an SiO₂/n-GaAs device show an absence of surface state related peaks and suggest that surface potential pinning under positive bias may be related to bulk states emerging at the surface.     

Monospecific antibodies as probes for the stoichiometry of recombinant GABA(A) receptors

GABA(A) receptors composed of alpha1beta3 gamma2 and alpha1beta3 subunits were expressed in insect Sf9 cells and solubilized in 1% Triton X100. In sucrose density gradients, [3H]-Ro15-1788 binding activity, in the case of alpha1beta3 gamma2, and [3H]-muscimol binding activity, in the case of alpha1beta3 containing receptors sedimented as a single sharp peak suggesting the formation of receptors containing a defined number of subunits. When alpha1beta3gamma2 -containing receptors were incubated with an alpha-subunit specific antibody (bd24), a single class of antibody receptor complex was formed irrespective of the receptor-antibody ratio. This is consistent with two alpha subunits cross-linked within the receptor by the antibody. Similar results were obtained using a beta-subunit specific antibody (bd17). Several classes of antibody-receptor complex were formed when receptors were pre-incubated with a gamma specific antibody (anti gamma(2) 1-15 Cys). This profile is consistent with the presence of a single gamma subunit in each complex. Experiments with alpha1beta3 subunit containing receptors and antibody bd24 produced a profile similar to that seen with alpha1beta3 gamma2 receptors, consistent with two alpha subunits per receptor complex. In this case, the anti-beta subunit antibody, bd17, produced a unique and complex profile consistent with three beta subunits per receptor. This method permits the rapid determination of subunit stoichiometries of homogeneous receptor populations     

Multiple trellis coded modulation (MTCM)

The authors demonstrate a trellis coded modulation technique referred to as multiple trellis coded modulation (MTCM) wherein more than one channel symbol per trellis branch is transmitted. They have found simple two-state trellis codes for symmetric MPSK multiple phase-shift keying and AM modulations that can achieve 3-dB gain over uncoded modulation at very high signal-to-noise ratios without bandwidth expansion or reduction in information bit rate. The gain of these codes with respect to previously reported two-state trellis codes is between 1 and 2 dB at very high signal-to-noise ratios, depending on the number of bits per Hertz transmitted. These gains are achieved for those of the equivalent conventional trellis codes with the same number of states in the trellis diagram. The authors note that additional computations per branch are needed for the multiple trellis coding scheme. The concept can be extended to a higher number of states and other types of modulations     

一种新的BOC(n,n)调制信号的无模糊度同步方法

针对现代GNSS中BOC(n,n)调制信号存在的模糊同步问题,在传统并行码相位捕获结构与码跟踪环的基础上进行改进,通过简单的本地码与重构方法提出一种新的BOC(n,n)的无模糊度同步方法。理论分析与仿真结果证明,该方法在保证BOC(n,n)无模糊捕获与跟踪的同时,具有传统同步处理结构简单易实现的特点,并具有良好的捕获与跟踪性能。通过比较去模糊度有效性、捕获概率、比例峰值、鉴相曲线与抗多径性能,证明文中方法相比经典的SPCP与ASPeCT具有更好的捕获与跟踪性能。     

A new class of signal constellations for differential unitary space-time modulation (DUSTM)

In this letter, a new class of signal constellations is proposed for differential unitary space-time modulation with multiple transmit antennas. In the proposed method, a rotation matrix is introduced to design signal constellations with large diversity product which is a primary property for signal constellations to have good performance in high signal to noise ratio (SNR).     

Differential pulse-code modulation (PCM) with entropy coding

As the transmission rateRgets large, differential pulse-code modulation (PCM) when followed by entropy coding forms a source encoding system which performs within 1.53 dB of Shannon's rate distortion function which bounds the performance of any encoding system with a minimum mean-square error (mmse) fidelity criterion. This is true for any ergodic signal source. Furthermore, this source encoder introduces the same amount of uncertainty as the mmse encoder. The 1.53 dB difference between this encoder and the mmse encoder is perceptually so small that it would probably not be noticed by a human user of a high quality (signal-to-noise ratio(S/N) geq 30dB) speech or television source encoding system.     

Adaptive modulation and coding (AMC) for bit-interleaved coded OFDM (BIC-OFDM)

This paper proposes adaptive modulation and coding (AMC) as a method for the bit-interleaved coded OFDM (BIC-OFDM) packet transmission. Following a pair-wise error probability (PEP) analysis of AMC-BIC-OFDM in a slowly fading frequency selective channel, AMC scheme maximizes the total rate by optimally selecting the code and efficiently allocating rate and power over the frequency band. The proposed method improves upon the performance of uniform rate and power allocation scheme by 6.5 to 10 dB     

A new pulse-width modulation (PWM) scheme for modular structured multilevel voltage source inverter

This work proposes a new switching scheme for a particular multilevel topology, known as the modular structured multilevel inverter (MSMI). The proposed scheme is based on symmetric regular sampled unipolar PWM, with multiple modulating waveforms and a single carrier. Mathematical equations that define the PWM switching instants are derived. These equations are suitable for digital implementation. An experimental five-level MSMI test-rig is built to implement the proposed algorithm. The derived equations are implemented by a low-cost fixed-point microcontroller. Several tests to quantify the performance of the inverter under the proposed modulation scheme are carried out.     

Phosphorylation of the 5-hydroxytryptamine3 (5-HT3) receptor expressed in HEK293 cells

The 5-hydroxytrptamine3 (5-HT3) receptor is a pentameric complex belonging to the family of ligand-gated ion channels. A variety of studies have suggested that phosphorylation regulates the rate of desensitisation and the size of amplitude of the receptor current. In this study we have examined the phosphorylation of the myc-tagged wild-type 5-HT3A receptor subunits from guinea-pig expressed in HEK293 cells (human embryonic kidney). Stably transfected cells were metabolically labelled with 32P-phosphoric acid. The results of immunoprecipitation and autoradiography demonstrate that both splicc variants of the 5-HT3A receptor subunit are phosphorylated in HEK293 cells. Site-specific mutagenesis revealed that phosphorylation occurs at serine 409, a potential target of protein kinase A. Thus the 5-HT3 receptor might be modulated by intracellular pathways, that allow variable 5-hydroxytryptamine action as responses to different extracellular stimuli.     

131 ps optical modulation in semiconductor multiple quantum wells (MQW's)

A new optical modulator has been fabricated which uses the recently discovered electroabsorption effect in MQW's. Optical pulses 131 ps long were generated when the device was driven with 122 ps electrical pulses. The input-output characteristics of the device show that it has low insertion loss with reasonable modulation depth and drive voltage.     

Compositional modulation in In(x)Ga(1-x)N: TEM and X-ray studies

Transmission Electron Microscopy (TEM) and X-ray diffraction (XRD) have been used to study compositional modulation in In(x)Ga(1-x) N layers grown with compositions close to miscibility gap. The samples (0.34 < x < 0.8) were deposited by molecular beam epitaxy using either a 200 nm thick AlN or GaN buffer layer grown on a sapphire substrate. Periodic compositional modulation leads to extra electron diffraction spots and satellite reflections in XRD in the theta-2theta coupled geometry. The ordering period delta measured along c-axis was about delta = 45 A for x = 0.5 and delta = 66 A for x = 0.78 for samples grown on AlN buffer layer. TEM and XRD determinations of delta were in good agreement. Compositional modulation was not observed for the sample with x = 0.34 grown on a GaN buffer layer. Larger values of delta were observed for layers with higher In content and for those having larger mismatch with the underlying AlN buffer layer. The possibility that the roughness of the AlN growth surface promotes strong In segregation on particular crystallographic planes leading to compositional modulation is considered.     

Complex meander pseudorandom code sequences and alternative binary offset carrier modulation (AltBOC modulation) in new-generation satellite navigation systems

Complex meander pseudorandom sequences (MPRSs) that are the basis for formation of alternative binary offset carrier modulated signals (AltBOC signals) for new-generation satellite radio navigation systems (in particular, the Galileo and Compass systems) are considered. The properties and characteristics of MPRSs are analyzed. Analytical expressions for the spectral densities and power spectrum densities of complex and complex conjugate meander symbols (MSs) of the MPRS of a ranging code are found for various values of the multiplicity coefficient of meander pulses. The modulating function of an elementary AltBOC signal is considered. The power spectrum densities of complex and complex conjugate MSs are plotted and analyzed for typical values of the multiplicity coefficient.     

Signal extraction with frequency arrangement (SEFA) andsuperimposed subcarrier modulation (SSM) schemes in fiber-orientedwireless access systems

This paper describes technologies for the improvement of the noise and nonlinearity characteristics of wireless access systems based on subcarrier optical transmission. First, the superimposed subcarrier modulation (SSM) technique is proposed to reduce the reflection noise induced by fiber connectors. We experimentally confirmed that the proposed method reduces this noise, and we found the optimum frequency and power of the superimposed subcarrier, SSM design methodology is also presented, taking both noise and nonlinearity into account. Second, signal extraction with frequency arrangement (SEFA) is proposed for increasing the optical modulation index, because the third-order intermodulation distortion (IM3) produced by the optical devices can be ignored. Simulation results show that SEFA greatly improves the transmission performance in terms of both the ratio of desired-to-undesired signal and the receiver sensitivity under Rayleigh fading. Combining the SSM and SEFA is also considered, for use with FP-LDs or DFB-LDs. These technologies will enable cheaper FP-LD implementation in fiber-oriented wireless access systems     

Optical phase modulators for MHz and GHz modulation in silicon-on-insulator (SOI)

This paper reports the simulation of the direct current (dc), transient, and optical characteristics of low-loss single-mode optical phase modulators based on silicon-on-insulator (SOI) material. The devices operate by injecting free carriers to change the refractive index in the guiding region and have been modeled using the two-dimensional (2-D) device simulation package SILVACO and the optical simulator BeamPROP to determine their electrical and optical performance, respectively. These simulators have been employed to optimize the overlap between the injected free carriers in the intrinsic region and the propagating optical mode. Attention has been paid to both the steady state and transient properties of the device. In order to produce quantitative results, a particular p-i-n device geometry has been employed in the study, but the trends in the results are sufficiently general to be of help in the design of many modulator geometries. The specific example devices used are designed to support a single optical guided mode and are of approximately 1 mm in cross-sectional dimensions. The modeling results predict that the transient performance of the device is affected significantly by the contact width and the rib doping depth. Results presented encompass Gaussian and constant doping profiles in the n/sup +/ regions. The doping profile of the contacts has a tremendous effect on both the dc and transient performances. Phase modulators with drive currents as low as 0.5 mA and transient rise times of 0.3 ns and fall times of 0.12 ns are predicted. Following from these results, a realistic doping profile is proposed that surpasses the electrical results of the Gaussian and most of the constant doping profiles. The improvements in electrical device characteristics are at the expense of a slightly increased optical absorption loss. An alternative switching technique is also presented that could further improve the device speed.     

Timing jitter and pump-induced amplitude modulation in thecolliding-pulse mode-locked (CPM) laser

The timing jitter and spurious amplitude modulation of colliding-pulse mode-locked (CPM) lasers were measured. The absolute jitter (the jitter of the laser alone) varied between 5 and 10 ps RMS in a 50-500-Hz bandwidth. The smallest measured relative jitter (timing fluctuations between the CPM and a radio-frequency (RF) synthesizer synchronized to the CPM) was 1.8 ps RMS in a 2-Hz to 1-kHz bandwidth. Separate from the jitter, spurious modulation in the CW pump laser mixes with the CPM pulse train to produce a set of discrete amplitude-modulated sidebands in the power spectrum of the CPM output. The frequencies of these sidebands change with cavity length, and the sidebands can be eliminated by operating the pump laser in a single longitudinal mode     

HDTV地面广播传输中的多载波(OFDM/COFDM)调制方案

介绍了在QPSK—OFDM传输试验中，在DTT中采用OFDM，对移动信源不必采用跟踪的定向天线，取而代之的是非定向天线和较少的接收基站就可以在多径环境中取得优良的性能。OFDM调制方案可以改善移动信源电视广播传播的操作，并在大规模传播中简化中继网络。     

GHz-bandwidth optical intensity modulation in self-poled waveguides in strontium barium niobate (SBN)

Wide-band electrooptic intensity modulation at a wavelength of 1.3 /spl mu/m has been demonstrated in single mode channel waveguides in SBN:60 without repoling the substrates after processing at elevated temperatures. Waveguide losses were /spl les/0.7 dB/cm for both polarizations.     

Analysis of cross-phase modulation (XPM) effect on WDM transmissionperformance

The authors analyse the effect of cross-phase modulation (XPM) on wavelength division multiplexing (WDM) transmissions by experiments and numerical simulations, and provide the XPM limitation in a normalised and closed form formula. They also investigate the effect of XPM on dispersion compensated transmissions. It is shown that the location of dispersion compensators and the amount of compensation should be determined by considering the XPM effect