一种利用CORDIC算法降低WiMAX系统峰均值功率比方法的研究及实现

基于802．16标准的微波存取全球互通（WiMAX）技术能够提供较高数据速率传输和较高的频谱利用率，并且实现简单，是宽带无线接入系统中最富有竞争力的技术之一。针对WiMAX系统中峰均值功率比（PAPR）过高的问题，从硬件实现的角度出发，利用协调旋转数字计算（CORDIC）算法来求出信号的幅度，采用限幅加滤波的方法来达到降低队PR的目的。实验结果表明这种方法在降低PAPR．值方面具有结构简单，效果良好的特点。     

基于ILLBP和ISSA的带钢表面缺陷识别

带钢表面缺陷存在着噪声、光照不均匀、纹理复杂以及局部区域对比度弱的问题。为此，提出了一种新的带钢表面缺陷识别算法。首先提出了ILLBP特征提取算法，在LBP算法中引入LTP的低阈值模式克服一定的噪声和光照影响，为了更好表征带钢表面缺陷复杂的纹理特征引入了ILBP中3种新的纹理结构，同时将LBP值的频率直方图改为了LBP局部梯度幅值和局部梯度方向的频率直方图，使其能更好地表征局部区域对比度强弱的关系；最后为了进一步提高带钢缺陷识别的准确率和减少冗余特征的影响，提出了一种改进的樽海鞘特征选择算法(ISSA)。在NEU数据集上仿真实验结果表明：算法(ILLBP+ISSA)能够克服光照不均匀、局部区域对比度弱、纹理复杂多样的影响，以及对噪声具有一定的鲁棒性。在高斯噪声信噪比为50 dB时带钢表面缺陷识别准确率能达到99.10%,40 dB时准确率能达到97.60%。     

3G网络中基于运动的位置更新算法研究

针对实际网络中存在大量的"乒乓"效应问题,分析了传统基于运动位置更新算法的不足,并提出了解决这一问题的有效算法.新算法增加了2个运动阈值,分别用来限制因局部蜂窝间往返运动和相邻位置区间的局部运动导致的位置更新次数,优化了传统算法中的运动阈值.在3G网络中3层数据库结构下对改进后的算法进行了仿真,并与传统算法进行了比较.结果表明,改进后的算法能有效抑制"乒乓"效应,并能降低平均位置更新次数.     

基于脉冲成型的降低FBMC系统峰均比方法

针对滤波器组多载波(FBMC:Filter Bank MultiCarrier)系统峰均比(PAPR:Peak to Average Power Ration)较高的问题,基于FBMC系统中原型滤波器及其多项结构,借鉴正交频分复用(OFDM:Orthogonal Frequency Division Multiplexing)降低峰均比方法,提出一种基于脉冲成型(PS:Pulse Shaping)技术的降低FBMC系统峰均比的方法.该方法在综合滤波器S/P(Serial to Parallel)后添加频率加权,实现了时域的循环位移,从而达到降低峰均比的目的.仿真结果表明,在FBMC系统中引入PS技术后,峰均比有明显下降.     

基于MSF的低复杂度chase型RS码软判决译码算法

重编码与坐标转换技术的应用,极大地降低了基于插值的RS(Reed-Solomon)码代数软判决译码算法的复杂度.基于采用这些技术后的插值二元多项式特征及译码信息多项式特征,提出一种混合多项式选择与因式分解方法(mix polynomial-selection and factorization,MSF),改变传统译码算法结构,以降低因式分解过程的平均算法复杂度.DEV C++程序仿真结果表明,与传统LCC(1ow-complexity chase)算法相比,在平均译码复杂度降低的情况下,且FER≤10-4时,RS(255,239),RS(63,55)能够获得0.1～0.2 dB的增益.     

弱磁场下研究掺杂微量Pr_2O_3的向列相液晶TEB30A薄膜的衍射

采用1.5 m W低功率的He-Ne激光(632.8 nm)正入射掺杂微量Pr_2O_3的向列相液晶TEB30A(TEB30A/Pr_2O_3)薄膜,研究在不同强度的弱磁场(0、0.4649 T、0.5062 T和0.5185 T)中的远场衍射特性。实验结果表明,在相同的条件下,当弱磁场强度超过一定的阈值时,在向列相液晶TEB30A中掺杂微量Pr_2O_3会非常明显地改善衍射图样的效果。基于Kirchhoff-Fraunhofe衍射积分原理的理论模拟结果表明,当磁场强度超过一定的阈值,微量Pr_2O_3掺杂之所以能明显地改善样品的衍射,是由于Pr_2O_3的掺杂增大了向列相液晶薄膜样品的非线性相移。TEB30A/Pr_2O_3薄膜的远场衍射消除了激光散度的影响。这一掺杂技术可应用于磁控光开关及光限幅等领域。     

基于驻极体静电俘能器的优化设计与实验测试

针对环境中的低频振动能量,建立了一种双端固支梁振动式驻极体静电俘能器理论模型.利用Matlab/Simulink数值仿真对静电俘能器的各项关键参数进行了优化.分别研究了静电俘能器的输出功率、谐振频率、半功率带宽与驻极体表面电位、空气间隙以及负载电阻的关系.在研究中,外部激励加速度幅值及驻极体尺寸保持恒定.数值分析结果如下:(1)存在一个最佳表面电位使得静电俘能器的输出功率达到最大值,随着表面电位的增加,软弹簧效应逐渐增强使得俘能器谐振频率发生偏移,半功率带宽逐渐增大.(2)当表面电位一定时,存在一个最佳初始空气间隙使得功率达到最大,随着间隙的增大,半功率带宽随之减小.(3)当表面电位和空气间隙保持一定时,存在一个最佳负载使得功率达到最大,随着负载的减小,谐振频率发生偏移.(4)当空气间隙一定时,存在一个最佳负载使得带宽达到最大,且表面电位越大,相同负载下的带宽越大.实验测试了不同负载电阻下俘能器的输出特性:输出功率及半功率带宽都随着负载电阻的增大,先增大而后减小.当负载电阻为90MΩ时,对应的最大输出功率为0.188 mW;当负载电阻为330 MΩ时,对应的半功率带宽达到最大值为4.7 Hz.     

LMS和RLS自适应滤波算法对比研究

介绍了自适应滤波器的基本原理,对最小均方(LMS,Least Mean Squares)和递归最小二乘(RLS,Recursive Least Squares)自适应算法进行仿真分析及对比研究.仿真结果及实例均表明,两种算法都能有效抑制和抵消各种干扰,但相比之下,RLS算法具有更好的收敛性能及稳定性.     

应用Khatri-Rao积分解的DS-CDMA盲多用户检测

对多用户直接序列码分多址(DS-CDMA)系统的多用户检测进行了研究,提出了一种基于Khatri-Rao积分解和连续干扰抵消的KRPSIC盲多用户检测算法.该算法充分利用DS-CDMA系统接收信号所具有的Khatri-Rao积结构性质,在用户扩频码、信道衰落系数均未知的情况下实现多用户检测,证明了算法的可辨识性和单调收敛性.仿真结果表明KRPSIC算法的误码率性能接近非盲的迫零算法,其作为一种非浅性迭代算法,在多用户检测的过程中对迭代初值的选取不敏感,当使用随机值初始化时算法依然有效.     

MMSE准则下基于玻尔兹曼机的快速重构算法

全连接的玻尔兹曼机模型可全面描述稀疏系数间统计依赖关系,但时间复杂度较高.为了提高基于玻尔兹曼机的贝叶斯匹配追踪算法(BM-BMP)的重构速度和质量,本文提出一种改进算法.第一,将BM-BMP算法的最大后验概率(MAP)估计评估值分解为上一次迭代的评估值与增量,使得每次迭代仅需计算增量,极大缩短了计算耗时.第二,利用显著最大后验概率估计值平均的方式,有效近似最小均方误差(MMSE)估计,获得了更小的重构误差.实验结果表明,本文算法比BM-BMP算法的运行时间平均缩短了73.66%,峰值信噪比(PSNR)值平均提高了0.57 dB.     

A novel Haar wavelet-based precoded BPSK-OFDM system with reduced PAPR

The performance of OFDM systems may be degraded when intersymbol interference (ISI) chan- nels have spectral nulls. Recently, the precoded OFDM was proposed to combat this problem. How- ever, due to inserting (M-K) zeros between each two sets of K consecutive information symbols, the average transmitting power of the precoded OFDM system reduces by 10log10 (M/K) dB com- pared with the conventional OFDM system. Under the same points inverse fast Fourier transformation (IFFT), the precoded OFDM system has a higher peak-to-average power ratio (PAPR) compared with the conventional OFDM system. This paper proposes a novel precoded BPSK-OFDM system based on Haar wavelet transformation. The Haar wavelet transformation operating decomposition over the vector information symbols produced by a precoder shows that half of the information symbols are zeros and the rest are either √2 or -√2.Then ,we have the peak power and PAPR reduced by 10log102≈3dB at most compared with the precoded OFDM system. Finally, we compare PAPR of the proposed OFDM system with the precoded OFDM and the conventional OFDM system.     

Interpretation of distortion product otoacoustic emission measurements. II. Estimating tuning characteristics using three stimulus tones

The simple model introduced in Part I [J. Acoust. Soc. Am. 102, 413-429 (1997)] is used to simulate the response of the cochlea to three stimulus tones. The focus is on "emission suppression tuning curves" constructed using a third tone to suppress the cubic distortion tone emission (CDT, 2f1-f2) generated by two primary tones at frequencies f1 and f2 (intensities L1 and L2). A criterion decrease (here, 5 dB) of the CDT emission amplitude defines the 2f1-f2 emission suppression tuning curve. Applying traditional tuning curve measures to emission suppression tuning curves appears ineffective in determining the underlying cochlear amplifier characteristics. However, it is shown that there are three characteristics of emission suppression tuning curves which are particularly useful: (1) the "f2 threshold" which is the level of the third tone, L3, required for the criterion CDT amplitude decrease, under the condition that the third tone frequency, f3, is approximately equal to f2; (2) the "shoulder threshold" similarly defined for f3 < f2; and (3) the "tuning width," w40. The tuning width is defined to be the distance (in octaves) from the frequency f2 to the upper f3 frequency for which there is a criterion CDT decrease, in this case using the L3 level which is 40 dB above the f2 threshold. Model calculations appropriate to gerbils show that these measures are most accurately related to the underlying cochlear amplifier characteristics for parameters where the primary stimulus amplitudes satisfy L1/L2 > 20 dB and for which L1 is 25 dB or more below the sharp "notch" seen in the two tone input-output function. In this parameter region, the cochlear amplifier characteristics are related to measured quantities by the relationships wr approximately equal to w40 and Ga approximately equal to TE + w40gp. Here, Ga is the gain (dB) of the cochlear amplifier, defined as the total increase in cochlear response over the passive response, wr is the distance (octaves) over which the active cochlear response rises to a maximum, and gp is the passive increase (dB/octave) of the traveling wave along the basilar membrane. The measured quantities are TE, the difference (dB) between the shoulder threshold and the f2 threshold, and the tuning width, w40 (octaves), defined above. Model predictions are confirmed by measurements in adult gerbils.     

Subcarrier and power allocation in OFDM-based cognitive radio networks

We formulate the subcarrier and power allocation problem in cognitive radio networks employing orthogonal frequency division multiplexing (OFDM) as a non-linear optimization problem with the objective of maximizing sum capacity under constraints of available subcarriers, interference temper- ature, power budget, etc. A close-to-optimal solution with much reduced complexity is proposed to separate the problem into two steps, which also considers fairness among secondary users. A fair al- gorithm for subcarrier allocation (FA_SA) is firstly presented. Secondly, a fast iterative water-filling algorithm for power allocation (FIWFA_PA) is also proposed to maximize the sum capacity. Exten- sive simulation results show that sum capacity performance of our low-complexity solution is very close to the optimal one, while significantly improving fairness and reducing computation complexity compared with the existing solutions.     

Effects of level and frequency on the detection of decrements and increments in sinusoids

Thresholds for the detection of decrements in level of sinusoidal signals were measured as a function of decrement duration, level (25, 40, 55, and 70 dB SPL) and frequency (250, 1000, and 4000 Hz) in eleven normally hearing subjects. Thresholds for detecting a brief increment in level were also measured. The sinusoids were presented in a background noise intended to mask spectral splatter associated with the decrement or increment. Performance tended to worsen with decreasing frequency, for all decrement durations and for increment detection. Performance also worsened with decreasing level. The results were analyzed using a model consisting of a compressive nonlinearity, a sliding temporal integrator, and a decision device. The analysis indicated that the worsening in performance with decreasing frequency and decreasing level can be attributed partly to increases in the equivalent rectangular duration (ERD) of the temporal integrator, but mainly to changes in the efficiency of the detection process following the temporal integrator; at lower frequencies and levels a larger change is required at the output of the integrator for threshold to be reached. At each frequency, the ERD was relatively invariant with level for levels more than about 20 dB above the absolute threshold.     

2f1-f2 distortion product otoacoustic emissions in White Leghorn chickens (Gallus domesticus): effects of frequency ratio and relative level

The effects of primary tone frequency ratio (f2/f1 ratio) and relative level (L2/L1) on the amplitude of the cubic difference tone (CDT: 2f1-f2) distortion product otoacoustic emissions (DPOAEs) were investigated in adult White Leghorn chickens (Gallus domesticus). In experiment 1, 9 f2/f1 ratios ranging from 1.05 to 1.8 were investigated. Measurements were obtained from both ears of 4 chickens at 7 f1 frequencies ranging from 0.8 to 4.0 kHz. The primary tones were equal in level, and varied from 20 to 80 dB SPL. The mean CDT amplitude increased with increasing primary tone level once the measurement noise floor was exceeded. The input/ output functions assumed one of two shapes: one in which there was a systematic increase in DPOAE amplitude with increasing primary tone level, and the other in which there was a plateau in the input/output function near 65-70 dB SPL. At the highest primary tone level (80 dB SPL), there was a decrease in the CDT amplitude with increasing f2/f1 ratio. At high primary tone levels, the f2/f1 ratio which produced the largest CDT was 1.05 or 1.1, while at lower primary tone levels the largest CDT occurred at f2/f1 ratios of 1.2-1.3. In experiment 2, L2 was held constant at 70 dB SPL, and L1 varied from 50 to 80 dB SPL. For f1 frequencies of 0.8 and 3.2 kHz, there was an increase in the CDT amplitude with increasing L1, followed by an asymptote at higher levels. In contrast, for 1.6 and 2.0 kHz f1 frequencies, the amplitude increased, plateaued and then increased again at higher levels. Informal measurements suggest that spontaneous otoacoustic emissions (SOAEs) are rarely seen in chickens. However, a reliable SOAE was observed in 1 chicken, which could be suppressed by external sounds and anoxia.     

A robust parametric estimator for single-trial movement related brain potentials

Current estimators for single-trial evoked potentials (EP's) require a signal-to-noise ratio (SNR) of 0 dB or better to obtain high quality estimations, yet many types of EP's suffer from substantially lower SNR's. This paper presents a robust-evoked-potential-estimator (REPE) facilitating high quality estimations of single movement related EP's with a relatively low SNR. The estimator is based on a standard ARX model, enhanced to support estimation under poor SNR conditions. The REPE was tested successfully on a computer simulated data set giving reliable single-trial estimations for the low SNR range of around -20 dB. THe REPE was also applied to experimental data, producing clear single-trial estimations of movement related brain signals recorded in a classic scenario of self-paced finger tapping experiment.     

Transient evoked otoacoustic emissions in patients with normal hearing and in patients with hearing loss

OBJECTIVES: 1) To evaluate transient evoked otoacoustic emission (TEOAE) test performance when measurements are made under routine clinical conditions. 2) To evaluate TEOAE test performance as a function of frequency and as a function of the magnitude of hearing loss. 3) To compare test performance using univariate and multivariate approaches to data analyses. 4) To provide a means of interpreting clinical TEOAE measurements. DESIGN: TEOAEs were measured in 452 ears of 246 patients. All measurements were made after acoustic immittance assessments, which were used to demonstrate that middle-ear function was normal at the time of the TEOAE test. TEOAE amplitudes and signal to noise ratios (SNRs), analyzed into octave bands centered at 1, 2, and 4 kHz, were compared with the pure-tone threshold at the same frequencies. Data were analyzed with clinical decision theory, cumulative distributions, discriminant analyses, and logistic regressions. RESULTS: Using univariate analysis techniques, TEOAEs accurately identified auditory status at 2 and 4 kHz but were less accurate at 1 kHz. Test performance was best when audiometric thresholds between 20 and 30 dB HL were used as the criteria for normal hearing. TEOAE SNR resulted in better test performance than did TEOAE amplitude alone; this effect decreased as frequency increased. Multivariate analysis methods resulted in better separation between normal and impaired ears than did univariate approaches, which relied on only TEOAE amplitude or SNR when test frequency band and audiometric frequency were the same. This improvement in test performance was greatest at 1 kHz, decreased as frequency increased, and was negligible at 4 kHz. CONCLUSIONS: TEOAEs can be used to identify hearing loss in children under routine clinical conditions. Univariate tests accurately identified auditory status at mid and high frequencies but performed more poorly at lower frequencies. The decrease in performance as frequency decreases may be a result of increased noise at lower frequencies but also may be due to properties of the measurement paradigm ("QuickScreen," high-pass filter at 0.8 kHz), which would not be ideal for recording energy around 1 kHz. The improvement in test performance when SNR was used and the interaction of this effect with frequency, however, would be consistent with the view that test performance in lower frequencies is at least partially influenced by the level of background noise. Multivariate analysis techniques improved test performance compared with the more traditional univariate approaches to data analysis. An approach is provided that allows one to assign measured TEOAE amplitudes, SNRs, or outputs from multivariate analyses to one of three categories: response properties consistent with normal hearing; results consistent with hearing loss; hearing status undetermined.     

Auditory frequency discrimination in the white rat

Frequency discrimination was investigated in the albino rat using a modified go/no-go positive reinforcement procedure in which subjects reported frequency increments in an ongoing series of pure tone bursts. Weber ratios (frequency difference limen/frequency) were measured from 5 to 32 kHz at 50 dB sound pressure level. A signal detection analysis of the procedure enabled a direct comparison to be made with the rat's performance in a discrete trial go/no-go task. A mean Weber ratio of 3.06+/-0.44% was measured in the frequency range 5-32 kHz. This indicates that the rat has better frequency discrimination acuity than has previously been thought. The result is discussed in the context of factors affecting performance. Among the factors that were explored we found that long training times and the specific training paradigm played important roles. In comparison to discrete trial go/no-go paradigms, rats performed much better when detecting signals from a repeating background. Frequency discrimination performance decreased linearly for tones less than 50 ms in duration. For longer tone duration performance was unaffected. The means and variability of reaction times for threshold changes of frequency were greater in comparison with supra-threshold frequency changes.     

Mechanical responses to two-tone distortion products in the apical and basal turns of the mammalian cochlea

Mechanical responses to one- and two-tone acoustic stimuli were recorded from the cochlear partition in the apical turn of the chinchilla cochlea, the basal turn of the guinea pig cochlea, and the hook region of the guinea pig cochlea. The most sensitive or "best" frequencies (BFs) for the sites studied were approximately 500 Hz, 17 kHz, and 30 kHz, respectively. Responses to the cubic difference tone (CDT), 2F1 - F2 (where F1 and F2 are the frequencies of the primary stimuli), were characterized at each site. Responses to the quadratic difference tone (QDT), F2 - F1, were also characterized in the apical turn preparations (QDT responses were too small to measure in the basal cochlea). The observed responses to BF QDTs and CDTs and to BF CDTs at each site appeared similar in many ways; the relative magnitudes of the responses were highest at low-to-moderate sound pressure levels (SPLs), for example, and the absolute magnitudes grew nonmonotonically with increases in the level of either primary (L1 or L2) alone. The peak effective levels of the CDT and QDT responses were also similar, at around -20 dB re L1 and/or L2. In other respects, however, the responses to CDTs and QDTs and to BF CDTs at each site behaved quite differently. At low-to-moderate SPLs, for example, most CDT phase leads decreased with increases in either L1 or L2, whereas most QDT phase leads increased with increasing L1 and varied little with L2. Most CDT responses also varied monotonically with equal-level primaries (i.e., when L1 = L2), whereas most QDT responses varied nonmonotonically. Different responses also varied in different ways when F1 and F2 were varied. Apical turn QDT responses were observed over a very wide F1/F2 range (F1 = 1-12 kHz), but were usually largest for stimuli <2-4 kHz. Apical turn CDT levels decreased (at rates of approximately 40-80 dB/octave) only when the frequency ratio F2/F1 increased beyond approximately 1.4-1.5. In the basal turn and hook regions, the CDT levels depended nonmonotonically on F2/F1 with the eventual rates of decrease being approximately 200 dB/octave. Optimal frequency ratios for the CDT increased from (F2 < 1.1F1) to (F2 approximately 1.2F1) with increasing SPL in the basal turn, but were stable at around F2/F1 approximately 1.05 in the hook region. CDT phase leads tended to increase with increasing F2/F1 in all three regions of the cochlea, particularly at low-to-moderate SPLs. These findings are discussed in relation to previous studies of cochlear mechanics, physiology, and psychophysics.