Conventional Detection Schemes Research Articles

Zero-field detection of spin dependent recombination with direct observation of electron nuclear hyperfine interactions in the absence of an oscillating electromagnetic field

Electrically detected magnetic resonance (EDMR) involves the electron paramagnetic resonance (EPR) study of spin dependent transport mechanisms such as spin dependent tunneling and spin dependent recombination (SDR) in solid state electronics. Conventional EPR measurements generally require strong static magnetic fields, typically 3 kG or greater, and high frequency oscillating electromagnetic fields, typically 9 GHz or higher. In this study, we directly demonstrate that, in the absence of the oscillating electromagnetic field, a very large SDR response (≈1%) can be detected at zero magnetic field with associated hyperfine interactions at extremely low magnetic fields in a silicon carbide (SiC) diode at room temperature. The zero-field SDR (ZFSDR) response that we detect is unexpected in the conventional detection scheme of SDR via EDMR. We believe that our observations provide fundamental physical understanding of other recently reported zero-field phenomena such as singlet triplet mixing in double quantum dots and low-field giant magnetoresistance in organic semiconductors. Our work provides an unambiguous demonstration that the zero-field phenomenon we observe involves SDR. Measurements reported herein indicate that extremely useful low-field SDR and ZFSDR results can be acquired simply and inexpensively in systems of technological importance. This work also suggests the potential use of this new physics in applications including absolute magnetometry with self-calibration, spin based memories, quantum computation, and inexpensive low-field EDMR spectrometers for wafer/probing stations.

Extended Detection for MIMO Systems with Partial Incremental Redundancy Based Hybrid ARQ

In this paper, an extended detection scheme is proposed for multiple-input multiple-output (MIMO) systems which employ partial incremental redundancy (IR) based hybrid automatic repeat request (HARQ). Based on the extended MIMO system model that interprets multiple retransmissions as a single transmission, the extended detection scheme estimates the entire transmitted symbols utilizing all information obtained up to the current retransmission. Compared with the conventional zero-forcing (ZF) detection scheme, the extended ZF detection scheme improves the post-processing signal-to-noise ratio (PSNR) of the newly transmitted symbols in every retransmission, as well as the repeatedly transmitted symbols. Simulation results verify that the extended detection scheme outperforms the conventional detection scheme. Simulation results also show that the extended minimum mean-square-error (MMSE) detection scheme can achieve a better error performance than the conventional maximum-likelihood (ML) detection scheme, and even the extended ZF detection scheme shows a comparable error performance to the conventional ML detection scheme.

Effective Two-Dimensional Partial Response Maximum Likelihood Detection Scheme for Holographic Data Storage Systems

An effective two-dimensional (2D) partial response maximum likelihood (PRML) detection scheme for holographic data storage (HDS) systems is proposed. The proposed scheme adopts the simplified trellis diagram, uses a priori information, and detects the data in two directions from the previously proposed detection schemes. The simplified trellis diagram which has 4 states and 8 branches yields a dramatic complexity reduction while the simplified 2D PRML detector shows serious performance degradation in the high density HDS channels. To prevent performance degradation, the proposed detector uses a priori information in order to give higher reliability to the branch metric. Furthermore, the proposed scheme detects the data in the vertical and horizontal directions to fully utilize the characteristics of the channel detection with a 2D partial response target. By effective combination of these three techniques, the proposed scheme with a simple structure has more than 2 dB gains compared to the conventional detection schemes.

Effective Two-Dimensional Partial Response Maximum Likelihood Detection Scheme for Holographic Data Storage Systems

An effective two-dimensional (2D) partial response maximum likelihood (PRML) detection scheme for holographic data storage (HDS) systems is proposed. The proposed scheme adopts the simplified trellis diagram, uses a priori information, and detects the data in two directions from the previously proposed detection schemes. The simplified trellis diagram which has 4 states and 8 branches yields a dramatic complexity reduction while the simplified 2D PRML detector shows serious performance degradation in the high density HDS channels. To prevent performance degradation, the proposed detector uses a priori information in order to give higher reliability to the branch metric. Furthermore, the proposed scheme detects the data in the vertical and horizontal directions to fully utilize the characteristics of the channel detection with a 2D partial response target. By effective combination of these three techniques, the proposed scheme with a simple structure has more than 2 dB gains compared to the conventional detection schemes.

Simplified maximum likelihood-based detection schemes for M-ary quadrature amplitude modulation spatial modulation

In this study, the authors propose a simplified maximum likelihood (ML)-based detection scheme for N t × N r M-ary quadrature amplitude modulation (M-QAM) spatial modulation (SM) that is computationally less complex than the conventional ML detection scheme. Instead of searching for the transmit antenna index and transmitted symbol pair among all possible N t M pairs as in the ML-based optimal detection, the proposed simplified ML-based detection scheme firstly searches for pairs of transmit antenna index and transmitted symbol in level-one subsets which the transmitted signal most probably belongs to, and secondly searches for pairs of transmit antenna index and transmitted symbol in level-two subsets among those pairs in level-one subsets. We also extend the simplified ML-based optimal detection into multistage detection. Simulation results validate that the bit error rate (BER) performance of the proposed simplified ML-based detection schemes is almost the same as that of conventional ML detection with significant complexity reduction until a BER of 10 -6 .

Asymptotic optimal detection for MIMO communication systems employing tree search with incremental channel partition preprocessing

The high complexity of optimal detection for spatial multplexing multiple-input multiple-output systems motivates the need for more practical alternatives. Among many suboptimal schemes reported in the literature, very few can be proven to provide close to optimal performance with low fixed complexity. The recently introduced Selection based Minimum Mean Square Error Ordered Successive Interference Cancellation (Sel-MMSE-OSIC) algorithm is one such scheme that employs list-based detection. Simulations results showed that its performance is nearly indistinguishable from optimal at almost all signal-to-noise ratio (SNR) levels. In this paper, we propose an improved asymptotically optimal fixed-complexity algorithm that provides substantial complexity reductions over Sel-MMSE-OSIC with similar error rate performance. This scheme is based on simplified channel partition and efficient tree-based list detection. To achieve further reductions in complexity for large constellation sizes, a variable complexity version of this scheme is proposed. The resulting algorithm is a variable complexity scheme that operates on a very small subset of candidates and employs an improved channel partition preprocessing that not only reduces complexity but also guarantees high SNR optimality over space uncorrelated channels. Simulations results confirm that the proposed scheme provides significant complexity reductions over conventional variable complexity detection schemes. Copyright © 2012 John Wiley & Sons, Ltd.

Spatio-temporally resolved detection on a microfluidic chip for monitoring the dynamic processes of molecular events

Detection is an essential aspect in analytical approaches. In liquid phase separations, many attempts have been focused on the capability to detect a partial or an entire column. However, detection in both spatial and temporal resolutions has not gained much attention yet. Here we present the concept of spatio-temporally resolved detection (STRD) and a proof-of-the-concept microchip electrophoresis (MCE)-STRD system. The MCE-STRD system was mainly composed of a microchip and an STRD unit, which were designed completely based on the requirements for spatial and temporal resolutions. In the STRD unit, a linear light beam expanded from a UV LED light source was employed to illuminate the whole separation channel of the microchip while a linear CCD sensor that has an identical effective length as the separation channel and more pixels per unit length was used to detect the absorbance signals through the separation channel. As each pixel of the CCD sensor can detect a corresponding channel space in real time, the CCD provides both spatial and temporal resolutions. A significant advantage of STRD over conventional detection schemes is its capability for monitoring the dynamic processes of molecular events occurring in the separation channel. This was demonstrated through the monitoring of the dynamic processes of protein-DNA and protein-drug interactions in chip isoelectric focusing (chip IEF). The MCE-STRD system provided not only whole pictures of the entire dynamic processes at-a-glance but also quantitative kinetic information (dissociation rate constants) of the dynamic processes. With further development, we anticipate that STRD could be a promising tool for the characterization of biomolecular interactions and the observation of migration behaviours of analytes.

Two alternative approaches to electro-optical detection of terahertz pulses

The electro-optical detection of terahertz radiation is analyzed theoretically. While a conventional detection scheme of this type is based on the measurement of the phase shift of an optical pulse arising from its interaction with the terahertz field in a nonlinear medium, it is shown that both the phase and amplitude of the optical pulse vary because of this interaction. The amplitude modulation carries information on the dynamics of the amplitude and phase of the terahertz field and can be used to measure these parameters. With this energy-sensitive detection scheme, avoiding all restrictions on the symmetry type of the nonlinear medium is much simpler than with the phase scheme. Variants of the electro-optical detection technique using periodically poled crystals with the lithium-niobate symmetry and crystals with the zincblende structure are considered. It is shown that spectral sensitivities of the methods based on measurements of the phase and amplitude modulations are related as the frequencies of the laser and terahertz fields.

Dipolar and quadrupolar detection using an FT-ICR MS setup at the MPIK Heidelberg

Dipolar and single-phase two-electrode quadrupolar detection schemes have been investigated at a Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) setup built for the KATRIN experiment at the Max-Planck-Institute for Nuclear Physics (MPIK) in Heidelberg. We present first experimental results of 7Li + signals from a cylindrical Penning trap configuration for both detection schemes. While the prominent signal of the conventional dipolar detection scheme marks the reduced cyclotron frequency, the main signal for the quadrupolar detection appears at the sum of the reduced cyclotron frequency and the magnetron frequency. For ideal trapping fields, this sum frequency equals the ion cyclotron frequency ν c = qB/(2πm). Sidebands due to the combined motions of the cyclotron mode and magnetron mode are observed by quadrupolar detection which allows the determination of the respective combinations of eigenfrequencies.

Efficient large core fiber-based detection for multi-channel two-photon fluorescence microscopy and spectral unmixing

Low-magnification high-numerical aperture objectives maximize the collection efficiency for scattered two-photon excited fluorescence (2PEF), but non-descanned detection schemes for such objectives demand optical components much bigger than standard microscope optics. Fiber coupling offers the possibility of removing bulky multi-channel detectors from the collection site, but coupling and transmission losses are generally believed to outweigh the benefits of optical fibers. We present here two new developments based on large-core fiber-optic fluorescence detection that illustrate clear advantages over conventional air-coupled 2PEF detection schemes. First, with minimal modifications of a commercial microscope, we efficiently couple the output of a 20×/NA0.95 objective to a large-core liquid light guide and we obtain a 7-fold collection gain when imaging astrocytes at 100 μm depth in acute brain slices of adult ALDH1L1-GFP mice. Second, combining 2PEF microscopy and 4-color detection on a custom microscope, mode scrambling inside a 2-mm plastic optical fiber is shown to cancel out the spatially non-uniform spectral sensitivity observed with air-coupled detectors. Spectral unmixing of images of brainbow mice taken with a fiber-coupled detector revealed a uniform color distribution of hippocampal neurons across a large field of view. Thus, fiber coupling improves both the efficiency and the homogeneity of 2PEF collection.

Recent results from HELIOS

Transfer and inelastic scattering reactions using light-ion beams and stable or long-lived targets have traditionally provided detailed information on the structure of nuclei near the line of beta stability. Such studies can now be extended to nuclei away from the line of β -stability as radioactive beams are becoming available at a number of facilities around the world, including the CARIBU facility at Argonne. These measurements must, however, be carried out in inverse kinematics, resulting in a loss of the effective experimental resolution when conventional detection schemes are employed. The HELIOS spectrometer is based on a new concept, that is especially well suited for such studies by reducing the resolution problem, providing simple particle identification, and giving high detection efficiency with moderate Si detector area. In this talk, the HELIOS concept and results from the first series of experiments will be presented.

MIMO Detection Schemes with Interference and Noise Estimation Enhancement

Different detection schemes for multiple-input, multiple-output (MIMO) systems are investigated. By enhancing the interference and noise estimation, we propose a novel MIMO receiver strategy, which is shown to achieve superior performance with moderate increase in computational complexity compared to conventional MIMO detection schemes.

A novel digital active homodyne demodulation scheme based on square‐wave phase modulation for interferometric fiber‐optic sensors

AbstractA novel digital active homodyne demodulation scheme to eliminate the signal fading in interferometric fiber‐optic sensors is proposed. The error signal is obtained by the square‐wave phase modulation and then the digital correlation detection technique is applied to demodulate the low‐frequency environmental phase drift and generate the offset phase, which is then fed back the integrated optical phase modulator to lock the interferometer in quadrature. The high‐frequency signal phase can be read out and recovered from the photodetector output with the interferometer in quadrature. The simulation and experimental results verify the feasibility of the proposed scheme, which obviates the feedback integrator saturation and the system resetting problem encountered in the conventional active homodyne detection schemes. © 2010 Wiley Periodicals, Inc. Microwave Opt Technol Lett 53:20–23, 2011; View this article online at wileyonlinelibrary.com. DOI 10.1002/mop.25640

EMCCD-based spectrally resolved fluorescence correlation spectroscopy

We present an implementation of fluorescence correlation spectroscopy with spectrally resolved detection based on a combined commercial confocal laser scanning/fluorescence correlation spectroscopy microscope. We have replaced the conventional detection scheme by a prism-based spectrometer and an electron-multiplying charge-coupled device camera used to record the photons. This allows us to read out more than 80,000 full spectra per second with a signal-to-noise ratio and a quantum efficiency high enough to allow single photon counting. We can identify up to four spectrally different quantum dots in vitro and demonstrate that spectrally resolved detection can be used to characterize photophysical properties of fluorophores by measuring the spectral dependence of quantum dot fluorescence emission intermittence. Moreover, we can confirm intracellular cross-correlation results as acquired with a conventional setup and show that spectral flexibility can help to optimize the choice of the detection windows.

Soft demodulation algorithms for orthogonally modulated and convolutionally coded DS-CDMA systems

A convolutionally coded M-ary orthogonal direct sequence code division multiple access (DS-CDMA) system in time-varying frequency-selective Rayleigh fading channels is considered in this work. We propose several novel soft demodulation algorithms based on interference cancellation and suppression techniques that can be coupled with soft decoding to improve the system performance in an iterative manner. The performance of the proposed demodulation algorithms is evaluated numerically and proved to achieve substantial bit error rate (BER) performance gain compared with the conventional detection schemes.

Nanowires As AFM Cantilevers: A Detection Scheme to Gently Image Soft Biological Materials in Fluids

Performing AFM on soft materials in fluids (e.g., living cells) is challenging due to their ready deformation by the tip. The thermal force-noise of the cantilever is the principal limitation to reducing sample deformation and minimizing a cantilever's cross- section reduces its noise significantly. However, the minimum size of the cantilever is currently limited by a conventional deflection detection scheme, which requires a large surface area for laser specular reflection. Here we develop an optical technique to use nanowires as cantilevers, and show that we achieve a force noise in water that is orders of magnitude gentler than conventional AFM. This is a significant milestone towards non-invasive scanning probe imaging of biological processes on the surfaces of vesicles and cell membranes.View Large Image | View Hi-Res Image | Download PowerPoint Slide

Quantum limited particle sensing in optical tweezers

Particle sensing in optical tweezers systems provides information on the position, velocity and force of the specimen particles. The conventional quadrant detection scheme is applied ubiquitously in optical tweezers experiments to quantify these parameters. In this paper we show that quadrant detection is non-optimal for particle sensing in optical tweezers and propose an alternative optimal particle sensing scheme based on spatial homodyne detection. A formalism for particle sensing in terms of transverse spatial modes is developed and numerical simulations of the efficacy of both quadrant and spatial homodyne detection are shown. We demonstrate that an order of magnitude improvement in particle sensing sensitivity can be achieved using spatial homodyne over quadrant detection.

Infrared spectroscopy for acetone and its dimer based on photoionization detection with tunable coherent vacuum-ultraviolet light

Infrared (IR) spectroscopy based on vacuum-ultraviolet (VUV) one-photon ionization detection is carried out for bare acetone and its dimer by use of tunable coherent VUV light. This is the first application of tunable VUV light to IR spectroscopy of a size-selected cluster, which has no suitable chromophore for conventional detection schemes. The advantage of this spectroscopic scheme is demonstrated. The observed IR spectrum of acetone dimer indicates formation of a C 2h symmetric structure, where the acetone molecules stack with an antiparallel orientation of the carbonyl groups.

An improved and efficient detection scheme for V-BLAST systems with QAM modulation

The paper proposed an improved Ordered Successive Interference Cancellation (OSIC) detection scheme for V-BLAST systems with square/rectangular Quadrature Amplitude Modulation (QAM) modulation. It utilizes an equivalent real-valued vector expression of relationship between transmit signals and received signals, exploits the constellation’s product-form structure and can eventually make the order, in which components of the transmit signals vector are extracted, more “optimal” in some sense. Thereby, it can offer an improved error probability as compared to the conventional OSIC detection scheme. In addition, the paper also proposes an efficient projection algorithm to calculate nulling vectors in a simple recursive fashion in order to avoid the vast increase of complexity, which is due to the fact that the original complex N-dimensional data vector and M × N channel matrix are transformed into a real 2N-dimensional data vector and a real 2M × 2N channel matrix respectively. A scrutinous complexity analysis shows that the complexity increases by only 33% as compared to the conventional scheme.

A Multipath Detection Scheme for CDMA Systems With Space–Time Spreading

Space-time spreading (STS) is an appealing open-loop transmit diversity scheme, which has recently been included into the cdma2000 standard. It has been shown that the performance of the STS scheme is highly sensitive to fading coefficient estimation errors, particularly when the channel is highly time dispersive. In practical systems, channel estimation is normally performed after the multipath components are resolved, which suggests that improving multipath detection reduces such estimation errors. Motivated by this, we address, in this paper, the problem of multipath detection in STS-based code division multiple access (CDMA) systems. We first extend the conventional energy-based multipath detection scheme (EMDS) to cope with the spatial channel structure. We derive approximate expressions for the probability of detection and probability of false alarm. It is shown that the errors produced by the conventional scheme in detecting the potential multipath components severely impact the performance of the receiver. To improve upon the EMDS, we introduce and analyze an improved multipath detection scheme (IMDS) based on the estimation of the interference power in the individual resolved multipath components. The efficacy of the proposed scheme stems from the fact that the interference in each potential path is estimated and subtracted before that path is detected. We also present a simple and realizable version of the proposed IMDS detection scheme. Our results show that the proposed scheme not only improves the bit-error-rate performance significantly but also utilizes the pilot power much more efficiently.