Active noise control: a tutorial review

Active noise control (ANC) is achieved by introducing a cancelling “antinoise” wave through an appropriate array of secondary sources. These secondary sources are interconnected through an electronic system using a specific signal processing algorithm for the particular cancellation scheme. ANC has application to a wide variety of problems in manufacturing, industrial operations, and consumer products. The emphasis of this paper is on the practical aspects of ANC systems in terms of adaptive signal processing and digital signal processing (DSP) implementation for real-world applications. In this paper, the basic adaptive algorithm for ANC is developed and analyzed based on single-channel broad-band feedforward control. This algorithm is then modified for narrow-band feedforward and adaptive feedback control. In turn, these single-channel ANC algorithms are expanded to multiple-channel cases. Various online secondary-path modeling techniques and special adaptive algorithms, such as lattice, frequency-domain, subband, and recursive-least-squares, are also introduced. Applications of these techniques to actual problems are highlighted by several examples     

Direct Graphical Determination of Optimum Shielding and Suppression

Signal parameters which will result in satisfactory levels of interference can be obtained directly from the graphs included in this paper. These graphs may be used to determine permissible waveforms for pulses, step functions, and CW signals for compliance with broad-band radiated, narrow-band radiated, and conducted interference limits. Curves are included for MIL-I-26600, MIL-I-6181D, MIL-I-11748, and MIL-STD-826. The curves are extremely simple for designers to use in determining shielding and suppression requirements. They may also be incorporated into the interference control plan to indicate to the customer that adequate interference control techniques will be incorporated.     

Performance improvement of a self-heterodyne detection BOTDR system employing broad-band laser

The self-heterodyne detection Brillouin optical time domain reflectometer (BOTDR) system using broad-band laser is proposed to reduce coherent Rayleigh noise and improve the system performance. Compared with the system with narrow-band laser, the stimulated Brillouin scattering (SBS) threshold can be improved by about 3 dB. The experimental results of the narrow-band laser measurements for three times independently and the broad-band laser measurement for one time are compared. The root-mean-square (RMS) errors of Brillouin linewidth for two systems with narrow-band laser and broad-band laser are 6.9 MHz and 2.7 MHz, respectively, and the RMS errors of temperature for the heated fiber are about 1.3 °C and 0.7 °C. With the broad-band laser, signal-to-noise ratio (SNR) of the unheated fiber is approximately equivalent to that of the integrated three independent Brillouin signals for the narrowband laser, and the results are believed to be beneficial for performance improvement and measurement time reduction.     

Compensating fiber gratings for source flatness to reduce multiple-access interferences in optical CDMA network coder/decoders

A fiber-Bragg-grating (FBG)-based optical code-division multiple-access (OCDMA) network coder/decoder (codec) is investigated for its interference suppression induced by nonflattened broad-band lightwave sources. Since each network user with different signature address code has different spectral distribution, the nonflattened light sources will cause multiple-access interference (MAI). Flatness compensation schemes are proposed to solve the MAI effects induced by nonflattened broad-band light sources. By arranging the same coding scheme but in different spectral coding band, spectral chips from FBG coder/compensator will incoherently power summed in the photodetectors to approach a more flattened power level. Signal-to-interference ratio (SIR) performances are evaluated with such compensation method for the discussed OCDMA network.     

Technical Considerations for Establishing Narrow-Band EMI Requirements for Data-Processing Equipment and Office Machines

Technology studies of the electromagnetic emanation charactersitics of electronic data processing (EDP) and office machine (OM) equipment was initiated within IBM about a decade ago. Since then, experimental and theoretical studies have been made of both radiated and conducted modes of electromagnetic propagation, and, in particular, the relationship of this propagation to communication receiver interference has been explored. This paper focuses on: 1) development of a worst-case narrow band interference model for most classes of communication services in the United States, and 2) a general approach to narrow band radiated and conducted limit setting. The low incidence of narrow band EDP interference problems is examined, and a statistical estimate of EMI is made for TV services (radiated) and AM radio (conducted). The significance of various limit levels is then discussed.     

用L阵实现频率、二维到达角和极化的联合估计

在宽频段内多信号多参量联合估计已成为许多研究课题（例如,未积压辐射源识别,有源对消等）的重要研究内容。对基于子空间方法的多信号频率、二维到达角和极化参量的联合估计方法进行了论述。该方法采用L阵和ESPRIT算法来实现,避免了平面阵的复杂性。计算机仿真结果证实了该算法的有效性。     

Capacity reduction of WCDMA downlink in the presence ofinterference from adjacent narrow-band system

One of the main challenges when implementing the future mobile multimedia networks is the cost-effective network evolution from second- to third-generation systems. This evolution path may include the use of different technologies at the same frequency band. The performance of the wide-band code-division multiple-access (WCDMA) downlink is studied in the case when there are narrow-band (NB) interference sources at the adjacent frequencies. A simple, analytical method to calculate the downlink capacity reduction of the WCDMA macrocell in this case is presented. The analysis takes into account different downlink interference mechanisms: wide-band noise from the transmitter as well as adjacent channel interference, intermodulation, and cross-modulation originating in the mobile receiver. The effect of each interference component to the capacity of the WCDMA macrocellular network has been evaluated with numerical examples. The analysis shows that capacity per cell is sensitive to the cell size, and therefore very careful network planning is needed in order to operate the WCDMA networks efficiently. The results of this paper can be utilized when implementing the WCDMA system to the same band with existing narrow-band systems, for instance, with the PCS 1900 band in United States and GSM 1800 band in Europe     

变换域窄带干扰抑制技术中变换基的选取研究

基于变换域窄带干扰抑制技术的基本思路,研究了几种常用变换基的性质及其对典型窄带干扰形式的识别能力。通过仿真对比了典型窄带干扰在各变换域的谱型,并以CV系数作为标准对各变换基窄带干扰抑制能力进行了比较。仿真结果表明,重叠变换对于单音、窄带等平稳干扰信号的识别能力较优,而对扫频干扰这种非平稳干扰类型,则更适合在分数阶傅里叶变换域进行检测和识别。     

一种新型的扩频通信自适应窄带干扰抑制技术

提出了1种基于IIR带阻滤波器的窄带干扰抑制方式,不但能够对窄带干扰进行精确的频率跟踪,而且能够根据信号电平自适应设置干扰的检测门限,并通过选择最佳的滤波器参数滤除干扰,从而可以将干扰造成的性能损失减小到最低程度,计算机仿真证实了本方法具有良好的窄带干扰抑制效果和较低的实现复杂度。     

On the use of a suppression filter for CDMA overlay

This paper is concerned with a direct-sequence code-division multiple-access (DS-CDMA) system operating over a Rayleigh fading channel and sharing a common spectrum with a narrow-band waveform. A suppression filter at the receiver is employed to reduce the narrow-band interference. We evaluate the average up-link bit error rate (BER) performance and investigate how the performance is influenced by various parameters, such as the number of taps of the suppression filter, the number of multiple-access users, the ratio of narrow-band interference bandwidth to the spread-spectrum bandwidth, the interference power to signal power ratio, the ratio of the offset of the interference carrier frequency from the spread-spectrum carrier frequency to the half spread-spectrum signal bandwidth, and so on     

分布式光纤光栅传感网络的复用解调技术

波长编码信号解调是实现光纤光栅多参量、多点分布式传感网络的核心技术之一。本文总结了光纤光栅传感信号解调的一般原理和技术难点,分类评述了常用解调方法的工作机理、特点和性能。同时,提出了一种新型的、用宽带光源和可调谐光滤波器(TOF)构成的可调谐窄带光源,对测量光栅阵列和参考光栅进行波长扫描,借助光电探测器和信号处理系统实现复用传感系统的解调技术。     

MMSE receiver for multicarrier CDMA overlay in ultra-wide-band communications

Multicarrier direct-sequence code-division multiple-access (MC-CDMA) overlay has been proposed to be used for ultra-wide-band (UWB) communications. Interference reduction and interference suppression are the key issues for sharing the spectrum in harmony between the established narrow-band systems and the overlaid UWB system. In this paper, investigation is carried out on the use of compromising measures incorporated to the MC-CDMA overlay to meet these goals, as well as on their impacts to the involving parties. At the transmitter, interference reduction to the established narrow-band systems is done by using notch filters. A multipath Nakagami fading channel is assumed. At the receiver, the interference suppression from those narrow-band systems is fulfilled by minimum mean square error (MMSE) detection technique. Numerical results show that precombining MMSE with selective-maximal combining provides the UWB system with much better performance than the receiver made up of notch filter in cascade with code correlator.     

Sensitivity of multiple-access techniques to narrow-bandinterference

This paper investigates the sensitivity of several multiple-access techniques to narrow-band interference. The analysis covers time-division multiple access (TDMA), code-division multiple access (CDMA), and orthogonal frequency-division multiple access (OFDMA). The study is carried out under the assumption that all the considered multiple-access systems occupy the same total bandwidth, and the bit rates of all active users are identical. A major finding of this study is that CDMA with pseudonoise spreading sequences is more sensitive to narrow-band interference than TDMA. We point out that the signal-to-jammer power ratio at the decision device input is in fact identical for both multiple-access techniques, but the amplitude distribution of the jammer term at the threshold detector input is more favorable to TDMA, which turns out to be more robust in terms of bit-error rate. Another finding is that in terms of sensitivity to narrow-band interference, orthogonal CDMA (OCDMA) is closer to TDMA than to CDMA with pseudonoise sequences, because the degradation is not the same for all users. Finally, we discuss the relationship of OCDMA and TDMA and highlight the superiority, in terms of capacity over the narrow-band interference channel, of TDMA to the other multiple-access techniques considered in this paper     

窄带CDMA系统无线规划的分析

本对窄带CDMA系统无线规划的一些关键问题如系统容量、链路预算、PN偏置、干扰隔离等做了比较详细的讨论。     

Optical code-division multiple access using broad-band parametrically generated light

A novel approach for an optical direct-sequence spread spectrum is presented. It is based on the complementary processes of broad-band parametric down-conversion and up-conversion. With parametric down-conversion, a narrow-band continuous-wave (CW) optical field is transformed into two CW broad-band white-noise fields that are complex conjugates of each other. These noise fields are exploited as the key and conjugate key in optical direct-sequence spread spectrum. The inverse process of parametric up-conversion is then used for multiplying the key by the conjugate key at the receiver in order to extract the transmitted data. A complete scheme for optical code-division multiple access (OCDMA) based on this approach is presented. The salient feature of the approach presented in this paper is that an ideal white-noise key is automatically generated, leading to high-capacity versatile code-division multiple-access configurations.     

Clipped Diversity Combining for Channels with Partial-Band Interference--Part I: Clipped-Linear Combining

Clipped-linear diversity combining is analyzed for receivers without side information. Communication systems with noncoherent demodulation, binary andM-ary orthogonal signaling, and diversity transmission are considered. The main source of interference is additive Gaussian partial-band interference, but a nonzero quiescent noise level is also included in the analysis to account for wide-band noise sources. Some of the results apply to general (non-Gaussian) interference. The numerical results demonstrate that clipped-linear combining can perform well in terms of both narrow-band interference rejection capability and maximum signal-to-interference ratio requirement. A practical disadvantage of clipped-linear combining is that it relies on measurements of the signal output voltage.     

多载波DS-CDMA系统抗干扰能力分析

结合并行转输和多载波调制技术，提出了一种多载波直接序列码分多址模型，对系统在存在窄带干扰的Rayleigh衰落信道下的性能进行了理论分析，并同Rake接收的单载波DS CDMA系统进行了比较。分析和仿真表明：该系统具有较强的抑制窄带及多址干扰的能力，同单载波DS CDMA系统相比，能支持更多的用户数。     

CDMA transmitter filtering for cellular overlay systems

In this paper, the overlay of a code-division multiple-access (CDMA) cellular system in a frequency band which is already providing service to a narrow-band cellular system is investigated. The motivation for this study is to demonstrate the potential of CDMA overlay as an efficient method for making a long-term transition from narrow-band cellular to CDMA cellular. For the single cell case, it was shown by Rainbolt and Miller (see IEEE J. Select. Areas Commun., vol.16, p.1756-64, 1998) that interference caused to the narrow-band system by even a lightly-loaded CDMA system is significant, a problem which can be greatly alleviated through the use of notch filtering in the CDMA transmitters to avoid active narrow-band users. Similar conclusions will be reached in this paper for the cellular case. The effects of notching on CDMA performance will be looked at in detail, and it will be shown that the notching is less of a problem than is the narrow-band interference inherent in overlay systems     

Deepen spectrum notch and reduce PAPR in OFDM systems via combining subcarriers precoding with tone reservation

In orthogonal frequency division multiplexing (OFDM) systems,spectrum notch can be generated to mitigate interference to other narrow-band services by turning off corresponding subcarriers.However,the inter-carrier interference may limit considerably the produced notch depth.Another problem in OFDM is the high peak-to-average power ratio (PAPR).In this paper,a technique combining subcarriers precoding with tone reservation is proposed to deepen spectrum notch and simultaneously reduce peak-to-average power ratio.Simulation results show that this presented joint algorithm can produce satisfied results to solve these problems at the expense of a moderate loss in bit error rate (BER) performance.