AFM/SCM及LBIC技术在平面型保护环结构InGaAs探测器设计中的应用

为研究保护环结构对平面型正照射式InP/InGaAs探测器光敏元扩大现象的抑制作用,设计并研制了带有不同保护环-光敏元间距的InGaAs探测器.通过原子力显微镜(AFM)及扫描电容显微镜(SCM)获得了保护环与光敏元之间的实际距离.利用激光束诱导电流(LBIC)技术研究了带有保护环结构的InGaAs探测器的光响应特性.研究表明,无保护环结构的探测器的LBIC信号可以用指数衰减函数描述,而带有保护环结构的探测器的LBIC信号则遵从高斯分布.引入保护环结构后,器件光敏元的扩大量会随着保护环-光敏元间距的减小而线性减小.在器件设计中,比较合适的保护环-光敏元间距应介于7~12μm之间.     

Efficient Implementation of Quasi- Maximum-Likelihood Detection Based on Semidefinite Relaxation

In this paper we develop two quasi-maximum likelihood (ML) channel detectors for multiuser detection: semidefinite relaxation (SDR) detector and phase-shift-keying (PSK) detector. These detectors can deliver near-ML bit error rate (BER) performance with a polynomial worst-case complexity. The SDR detector for binary-phase-shift-keying (BPSK) constellation is based on a convex SDR, whereas the PSK detector for $M$-PSK constellations is based on a nonconvex low-rank SDR. The SDR detector is implemented using a dual-scaling interior-point method, while the PSK detector is based on a coordinate descent strategy on a feasible region homotopy. We use dynamic dimension reduction and warm start techniques to achieve signal-to-noise ratio (SNR)-sensitive improvements for both detectors. Numerical simulations of BER performance and running time indicate the effectiveness of the two quasi-ML detectors when compared to the conventional sphere decoder and its variants.      

Physical structure of molecular-beam epitaxy growth defects in HgCdTe and their impact on two-color detector performance

The flexible nature of molecular-beam epitaxy (MBE) growth is beneficial for HgCdTe infrared-detector design and allows for tailored growths at lower costs and larger focal-plane array (FPA) formats. Control of growth dynamics gives the MBE process a distinct advantage in the production of multicolor devices, although opportunities for device improvement still exist. Growth defects can inhibit pixel performance and reduce the operability in FPAs, so it is important to understand and evaluate their properties and impact on detector performance. The object of this paper is to understand and correlate the effects of macrodefects on two-color detector performance. We observed the location of single-crystal and polycrystalline regions on planar and cross-sectioned surfaces of two-color device structures when void defects were viewed by scanning electron microscopy (SEM). Compositional analysis via energy dispersive x-ray analysis (EDXA) of voids in the cross section showed elevated Te and reduced Hg when compared to defect-free growth areas. The second portion of this study examined the correlation of macrodefects with pixel operability and diode current-voltage (I–V) characteristics in mid-wavelength infrared (MWIR)/MWIR (M/M) and long wavelength infrared (LWIR)/LWIR (L/L) two-color devices. The probability of diode failure when a void is present is 98% for M/M and 100% for L/L. Voids in two-color detectors also impact diodes neighboring their location; the impact is higher for L/L detectors than M/M detectors. All void-containing diodes showed early breakdown in the I–V characteristics in one or both bands. High dislocation densities were observed surrounding voids; the high density spread further from the void for L/L detectors compared to M/M detectors.     

Two-stage Wilcoxon detectors using conditional tests

The idea of the Wilcoxon detector using a conditional test is extended to two-stage detectors, which constitute a class of sequential detectors. Three different two-stage detectors are considered, using the Wilcoxon statistic with conditional tests. The three detectors differ in the usage of the samples of the first stage for computing the test statistic in the second stage. In computing the test statistic in the second stage, the first detector disregards all the samples of the first stage, the second detector uses the value of the test statistic of the first stage, and the third detector uses all the samples of the first stage. The asymptotic relative efficiency improves from the first to the second detector. Comparisons of these detectors with fixed-sample-size (FSS) detectors show that they are better than both the FSS linear detector and the FSS conditional Wilcoxon detector under the same false-alarm and detection probabilities     

锰钴镍铜氧薄膜红外探测器制备与性能研究

报道了锰钴镍铜氧薄膜（Mn1.56Co0.96-xNi0.48CuxO4,MCNC,x=0,0.08,0.16,0.24）的红外探测器件的制备过程及器件性能。通过改变掺杂Cu的比例,制作了系列MCNC薄膜材料及红外探测器件。实验结果表明,对于一定厚度及尺寸的薄膜器件,铜的掺入能显著减小器件的阻值及器件噪声,弥补了负温度系数的减小的缺点。器件时间常数约为20~40ms。掺铜量为0.24的薄膜器件的探测率为0.83107cmHz1/2W-1,相比同样规格的锰钴镍器件提高了约130%。此外,对于MCNC薄膜器件的老化现象进行了初步探讨。     

威伯尔和对数正态噪声中的检测问题

本文研究窄带非高斯(non-Gaussian)噪声中窄带相参和非相参脉冲串信号的离散时间检测。导出了局部最佳(LO)检测器结构,它具有在窄带高斯噪声中的尼曼-皮尔逊(Neyman-Pearson)最佳检测器里引入局部最佳零记忆非线性(LOZNL)的形式。许多实用检测器属于与LO检测器相同类型的结构,导出了这些检测器功效的表达式,特别研究了威伯尔(Weibull)和对数正态噪声模型。导出了LOZNL和检测器功效,并用曲线给出了数值结果。说明在皮特曼(Pitman)的渐近相对效率(ARE)意义上,许多具有能更多抑制噪声包络分布尾部的非线性的检测器,其渐近性能明显优于窄带高斯噪声中的尼曼-皮尔逊最佳检测器。     

OSSO和OSGO恒虚警检测器在Pareto分布混响背景下的性能分析

Pareto分布是一种重要的非高斯分布,被证明能够有效描述高分辨率主动声纳的混响统计特性。文章分析了有序统计选小(Ordered Statistic with Smallest Option, OSSO)和有序统计选大(Ordered Statistic with Greatest Option, OSGO)两种恒虚警(Constant Fales Alarm Rate, CFAR)检测器在Pareto分布混响背景下的性能。在尺度参数已知情况下,证明了OSSO-CFAR和OSGO-CFAR对形状参数具有恒虚警的特性。进一步分析了两种检测器在均匀Pareto混响背景、多目标干扰及混响边缘情况下的性能,并与有序统计(Ordered Statistic, OS)CFAR进行了对比。结果表明,在均匀混响背景下,OSGO-CFAR的检测性能与OS-CFAR相近,在混响边缘情况下具有最好的虚警控制能力;而对于多目标干扰情况,OSSO-CFAR比其他两种检测器的检测性能更优。      

Detection in weibull and log-normal noises

The discrete-time detection of narrowband coherent and incoherent pulse train signals in narrowband non-Gaussian noise is investigated. The locally optimum (LO) detector structures are developed and found to be in the form of incorporating a locally optimum zero-memory nonlinearity (LOZNL) into the Neyman-Pearson optimum detector for narrowband Gaussian noise. Many practical detectors belong in the same class of structures with the LO detector. The expressions for the efficacies of the detectors are derived. In particular, Weibull and log-normal noise models are considered. The LOZNL’s, and the efficacies of the detectors are given, and numerical results are graphically presented. It is shown that, in the sense of the Pitman asymptotic relative efficiency (ARE), the asymptotic performance of many detectors whose nonlinearity can more effectively suppress the tail of the noise envelope distribution is apparently better than that of the Neyman-Pearson optimum detector for narrowband Gaussian noise.     

Blind Receiver Design for OFDM Systems Over Doubly Selective Channels

We develop blind data detectors for orthogonal frequency-division multiplexing (OFDM) systems over doubly selective channels by exploiting both frequency-domain and time-domain correlations of the received signal. We thus derive two blind data detectors: a time-domain data detector and a frequency-domain data detector. We also contribute a reduced complexity, suboptimal version of a time-domain data detector that performs robustly when the normalized Doppler rate is less than 3%. Our frequency-domain data detector and suboptimal time-domain data detector both result in integer least-squares (LS) problems. We propose the use of the V-BLAST detector and the sphere decoder. The time-domain data detector is not limited to the Doppler rates less than 3%, but cannot be posed as an integer LS problem. Our solution is to develop an iterative algorithm that starts from the suboptimal time-domain data detector output. We also propose channel estimation and prediction algorithms using a polynomial expansion model, and these estimators work with data detectors (decision-directed mode) to reduce the complexity. The estimators for the channel statistics and the noise variance are derived using the likelihood function for the data. Our blind data detectors are fairly robust against the parameter mismatch     

Large-sample performance of blind and Group-blind multiuser detectors: a perturbation perspective

In blind and group-blind multiuser detection, different detectors can be designed using either the sample data covariance matrix directly or its eigencomponents. Due to finite-sample effect in practice, their performance deviates from the corresponding optimum. A perturbation technique is developed rigorously and systematically to analyze those detectors in this work. Subject to the assumption that the first-order perturbation dominates, corresponding results can be applied to a practical system of a given sample size. In particular, performance of the following typical detectors is studied for either flat or estimated multipath channels: direct-matrix-inversion (DMI) blind minimum mean-square error (MMSE) detector, subspace blind MMSE detector, direct zero-forcing (ZF) detector, subspace ZF detector, and group-blind hybrid detector. Simulation examples further verify various analytical results.     

Reduced-dimension MAP turbo-BLAST detection

The Bell Labs layered space-time (BLAST) architecture is a simple and efficient multiantenna coding structure that can achieve high spectral efficiency. Many BLAST detectors require more receiver antennas than transmitter antennas. We propose two novel turbo-processing BLAST detectors that can operate in systems with fewer receiver antennas than transmitter antennas. Both detectors are based on the group-detection strategy. The first proposed detector, the reduced-dimension maximum a posteriori (RDMAP) detector uses a dynamically formed group for each bit decision, while the second proposed detector, the group maximum a posteriori (GMAP) uses a static grouping. For both detectors, a maximum a posteriori (MAP) decision is made using a group of transmitted symbols, and the remaining signal contribution is treated as interference. The interference is characterized as nonzero mean colored-noise source that is whitened before a decision is made. Both proposed detectors are generalizations of the MAP detector and the turbo-processing minimum mean-squared error (MMSE) detector in Sellathurai and Haykin, and Abe and Matsumoto. An uncoded bit-error rate analysis for an independent Rayleigh fading environment is also presented. Simulated results are presented which show that both the RDMAP and GMAP detectors have a performance improvement over the MMSE detector, especially in systems having an excess number of transmitter antennas.     

Parallel group detection for synchronous CDMA communication overfrequency-selective Rayleigh fading channels

A group detector jointly detects a group of users, and a parallel group detection scheme is a bank of J independently operating group detectors, one for each group of a J group partition of the K transmitting users of a code-division multiple-access (CDMA) channel. In this paper, two group detectors are introduced for the frequency-selective Rayleigh fading (FSRF) CDMA channel. While the optimum multiuser detector has a time complexity per symbol (TCS) of O(M ^K/K) for M-ary signaling, each of the two group detectors has a TCS of O(M(|G|)/|G|) where |G| is the group size. Hence, there are parallel group detection schemes, based on each of the two group detectors, that satisfy a wide range of complexity constraints that result from the choice of partition. Each of the two group detectors is minimax optimal in the corresponding conditional group near-far resistance measure. Furthermore, a succinct indicator of the average BER over high SNR regions is defined via the asymptotic efficiency. A lower bound and an exact formula for the asymptotic efficiency are derived for the first and second group detectors, respectively. The group detection approach for the FSRF-CDMA channel generalizes previous approaches to the complexity-performance tradeoff problem. It yields the optimum detector when the group size is K. When the group size is equal to one, the first group detector results in a new optimum linear detector and the second reduces to a recently proposed suboptimum linear detector. All other nontrivial partitions yield new multiuser detectors whose performances are commensurate with their complexities     

相关高斯噪声自适应非参量检测器

本文讨论了相关高斯噪声自适应非参量检测器。当输入噪声的采样满足独立、同分布(IID)条件时,不管分布是什么形式,非参量检测器均能保持虚警概率恒定(CFAR)。但是,许多类噪声并不能保持IID条件,检测器也就无法保持CFAR。本文提出一种简单、可行的自适应非参量检测器,能自动调节门限,使虚警概率(Pfa)趋于恒定。这种方法的关键在于用递归滤波器的输出值来测量噪声的相关系数(Pd),并由此改变秩值检测器的检测单元的权,使其Pfa趋于恒定。从而使在一定信噪比条件下发现概率(Pd)也趋于恒定。本文给出检测单元加权的非参量检测器的检测性能和渐近性能,然后还给出自适应非参量检测器的近似计算方法和计算机模拟结果。     

Quasi-maximum-likelihood multiuser detection using semi-definiterelaxation with application to synchronous CDMA

The maximum-likelihood (ML) multiuser detector is well known to exhibit better bit-error-rate (BER) performance than many other multiuser detectors. Unfortunately, ML detection (MLD) is a nondeterministic polynomial-time hard (NP-hard) problem, for which there is no known algorithm that can find the optimal solution with polynomial-time complexity (in the number of users). A polynomial-time approximation method called semi-definite (SD) relaxation is applied to the MLD problem with antipodal data transmission. SD relaxation is an accurate approximation method for certain NP-hard problems. The SD relaxation ML (SDR-ML) detector is efficient in that its complexity is of the order of K^3.5, where K is the number of users. We illustrate the potential of the SDR-ML detector by showing that some existing detectors, such as the decorrelator and the linear-minimum-mean-square-error detector, can be interpreted as degenerate forms of the SDR-ML detector. Simulation results indicate that the BER performance of the SDR-ML detector is better than that of these existing detectors and is close to that of the true ML detector, even when the cross-correlations between users are strong or the near-far effect is significant     

ADAPTIVE NONPARAMETRIC DETECTOR ON CORRELATION GAUSSIAN NOISE

The problem of adaptive nonparametric detector in correlation Gaussian noise isconsidered.The nonparametric detectors are CFAR(Constant-False-Alarm-Rate)detectors,whenthe input received reference cells are IID(Identical Independent Distribution)variances.But the falsealarm probability(P_(fa))of the nonparametric detectors could not be constant if the samples of thereference range cells are not independent.A simple and easily implemented adaptive nonparametricdetection method is proposed in the paper.In orde to maintain CFAR the weight of the detection rangecell of the detector must be changed by different output values of the IIR filter for measurement of thecorrelation coefficient(p)of the input noise.In this paper the closed form expressions for detectionprobability(P_d)and P_(fa)of the weighted nonparametric detector are derived.The ARE(AsymptoticRelative Efficiency)of the weighted detectors is investigated.In the end the detection performance ofthe adaptive nonparametric detector is determined by Monte Carlo simulation on the digital computer.     

OSGO-CFAR在K分布杂波边缘中的性能分析

研究有序统计选大（OSGO）恒虚警检测器在K分布杂波边缘中的性能。文中推导出了该检测器在K分布杂波边缘中虚警概率的解析表达式，分析了它抗干扰边缘的性能，并与OS、CA、OSSO等检测器进行了比较，结果表明OSGO-CFAR具有最好的抗K分布杂波边缘的性能。     

Performance of blind and group-blind multiuser detectors

In blind (or group-blind) linear multiuser detection, the detector is estimated from the received signals, with the prior knowledge of only the signature waveform of the desired user (or the signature waveforms of some but not all users). The performance of a number of such estimated linear detectors, including the direct-matrix-inversion (DMI) blind linear minimum mean square error (MMSE) detector, the subspace blind linear MMSE detector, and the form-I and form-II group-blind linear hybrid detectors, are analyzed. Asymptotic limit theorems for each of the estimates of these detectors (when the signal sample size is large) are established, based on which approximate expressions for the average output signal-to-interference-plus-noise ratios (SINRs) and bit-error rates (BERs) are given. To gain insights on these analytical results, the performance of these detectors in an equicorrelated code-division multiple-acces (CDMA) system is compared. Examples are provided to demonstrate the excellent match between the theory developed here and the simulation results     

Asymptotically optimum finite-memory detectors in φ-mixingdependent processes

The design of a finite-memory partition system for the detection of a constant signal in φ-mixing noise is investigated. It is found that the new detector converges to the locally optimal finite-memory practically intractable detector characterized by a multidimensional Fredholm integral equation of the second kind. The new detector encompasses many classes of known detectors. Numerical calculations demonstrate that the finite-memory detector compares favorably, using asymptotic relative efficiency as a fidelity criterion, to other classes of detectors even if extremes of dependent noise distributions are considered. The same calculations also suggest that a dependent process may be treated as an M-dependent process in finite-memory detectors without causing significant detrimental effects, provided M is sufficiently large. To reduce excessive computational complexity, a priori knowledge regarding properties of system parameters (such as matrix symmetry) as well as noise distributions (especially Gaussian and its independently nonlinear transformations) are exploited. Generalizations and extensions of the proposed detectors are also discussed. The operation of the detector may be easily extended to include adaptability and/or sequential operation     

Genetically modified multiuser detection for code division multipleaccess systems

The problem of multiple access interference (MAI) and intersymbol interference (ISI) suppression in code division multiple access (CDMA) systems is considered. By combining the theory of multiuser detection (MUD) and evolutionary computation, a hybrid genetic engine is proposed, suitable for the detection of CDMA signals in the presence of MAI and ISI. The proposed hybrid detector structure can be extended to most multiuser detectors and used as the base detector within the structure. Using random selection, mutation and crossover operators and a unique chromosome structure, the genetic algorithm evolves the base detector to a group of more efficient detectors in terms of bit-error rate performance. First, a new packet-level genetic MUD technique, using a conventional single user detector as the base detector, is proposed for asynchronous CDMA (ACDMA) with negligible ISI. Then the signal-subspace-based minimum mean square error detector is chosen as a base detector and wrapped inside the hybrid genetic engine to evolve to a better structure nearly to eliminate both ISI and MAI. The novelty of the proposed structure is the way the deterministic closed-form solution of the base detector is mapped to a genetic engine resulting in a group of more efficient and adaptive detectors     

Group detection for synchronous Gaussian code-divisionmultiple-access channels

The concept of group detection Is introduced to address the design of suboptimum multiuser detectors for code-division multiple-access (CDMA) channels. A group detection scheme consists of a bank of P group detectors, one each for detecting the information symbols of users in each group of a P group partition of the K simultaneously transmitting users. In a parallel group detection scheme, these group detectors operate independently, whereas in a sequential scheme, each group detector. Uses the decisions of the previous group detectors to successively cancel the interference from those users. Group detectors based on the generalized likelihood ratio test (GLRT) are obtained for the synchronous Gaussian CDMA channel. The complexity of these detectors is exponential in the group size, whereas that of the optimum detector is exponential in K. Since the partition of users is a design parameter, group sizes can be chosen to satisfy a wide range of complexity constraints. A key performance result is that the GLRT group detectors are optimally group near-far resistant. Furthermore, upper and lower bounds on the asymptotic efficiency of the sequential group detectors are derived. These bounds reveal that the sequential group detectors can, under certain conditions, perform as well as GLRT group detectors of much larger group sizes. Group detection provides a unifying approach to multiuser detection. When the users are partitioned into K single-user groups, the GLRT, a modified form of GLRT, and the sequential group detectors reduce to previously proposed suboptimal detectors; namely, the decorrelator, the two-stage detector, and the decorrelating decision-feedback detector, respectively. For the other nontrivial partitions, the group detectors are new and have a performance that is commensurate with their complexity