伪码调相连续波引信压制式宽带干扰抑制的包络滤波方法

该文分析了几种典型压制式宽带干扰(BPSK干扰、调频干扰)对伪码调相连续波引信相关输出的影响。分析发现当干扰强度超出伪码调相引信的抗干扰容限时,其相关输出严重恶化,因此必须在相关检测前对上述干扰进行抑制。提出了一种通过包络滤波的宽带干扰抑制新方法。接收信号经过正交解调输出I,Q两路信号,由I,Q两路分量获得解调信号的瞬时包络和瞬时相位。包络序列在变换域通过门限滤波去除有用信号和白噪声成分从而得到干扰信号包络。利用滤波后的包络和瞬时相位重构出干扰同相信号,最后将干扰信号从I路放大信号中去除即得到所需信号。仿真分析发现该方法能较好地抑制干扰,尤其是对强干扰,相关输出得到明显改善。该方法计算简单,易于理解,容易工程实现。     

Recursive algorithms for identification of impulse noise channels

The Class A Middleton model is a widely accepted statistical-physical parameteric model for impulsive interference superimposed on a Gaussian background. In the present work, a recursive decision-directed estimator for online identification of the parameters of the Class A model is proposed. This estimator is based on an adaptive Bayesian classification of each of a sequence of Class A envelope samples as an impulsive sample or as a background sample. As each sample is so classified, recursive updates of the estimates of the second moment of the background component of the interference envelope density, the second moment of the impulsive component of the interference envelope density, and the probability with which the impulsive component occurs, are readily obtained. From these estimates, estimates of the parameters of the Class A model follow straightforwardly, since closed-form expressions for the parameters exist in terms of these quantities. The performance characteristics of this algorithm are investigated and an appropriately modified version is found to yield a recursive algorithm with excellent global performance     

Approximate band-pass limiter envelope distributions

An approximate distribution is computed for the envelope of sine wave plus noise after passage through a wide-band filter, limiter, and narrow-band filter. It is shown that as the input bandwidth to the limiter increases, the output envelope distribution converges to the usual sine wave in noise envelope distribution, without limiting, but with a definite1.04db loss. First-order correction terms are supplied which make it possible to compute first-order statistics for the output envelope when the output signal-to-noise ratio is on the order of one.     

Development and Description of an Output Criteria Function and Performance Measure

The problem is that of predicting interference focuses on 1) the equipment output in the presence of interference, and 2) the relation between a given output and the equipment performance. To designate the investigation of an equipment output in relation to the device performance, we use the term output criteria. Output criteria are methods for evaluating system device outputs relative to prescribed standards. This paper introduces a method for obtaining such criteria. This paper defines a function for the output criteria in terms of the various elements that would exist in any general interference situation. The desired function yields a performance measure expressed in general system performance terms (e.g., percent system efficiency). This report also notes certain instances in which currently used criteria correspond to portions of the overall performance measure described. The various elements used in the performance measure are also discussed in terms of their interrelationships as well as their meaning relative to physically significant interference situations. A hypothetical signal and interference environment is described and a matrix is defined which describes 1) all the signal and interference combinations under consideration, and 2) for each specific signal and interference combination, the various decisions which could be made at the equipment output regarding the signal and interference believed to have been present. The decision matrix is used to define the events for which cost estimates must be made.     

A two-sensor array blind beamformer for direct sequence spreadspectrum communications

We present an efficient blind beamformer dedicated to the problem of interference mitigation in direct sequence spread spectrum (DSSS) communication systems using a two-sensor array. A closed-form solution for the blind identification of the communication channel is derived by exploiting the temporal properties of the desired signal and the interference. The optimal beamformer is derived from the maximization of the signal-to-interference and noise ratio (SINR) at the output of the receiver in terms of the blindly estimated channel coefficients. Three structures of the DSSS receiver are presented. One structure consists of the blind beamformer followed by the spread spectrum demodulator. The other two structures consist of the spread spectrum demodulator followed by the blind beamformer. The performance of these structures is discussed in terms of the achieved SINR and the computational cost. Simulation results are provided to illustrate the effectiveness of the proposed blind beamformers in interference excision     

基于小波变换的干涉信号包络提取方法研究

为了实现对宽谱光源自相干函数的测量,必须对宽谱光源干涉信号的包络进行提取.因此,宽谱光源干涉信号包络的提取就成为了测量光源自相干函数的关键因素.针对现有的包络解调方法的不足,建立了基于复Morlet小波的干涉信号包络提取方法.该方法采用复Morlet小波作为母小波,通过选择适合尺度参数和位置参数,可以有效地提取干涉信号的包络并具有良好的抗噪能力;利用计算机Matlab仿真证明了该方法的有效性;最后利用该方法对韩国Fiber Pro公司的白光干涉仪干涉输出信号进行包络提取,动态范围达到-60 dB.     

On the rms bandwidth of nonlinearly envelope detected narrow-band Gaussian noise

This paper determines the relationship between the rms bandwidth of the envelope of a narrow-band Gaussian process and the rms bandwidth of the process itself for a general nonlinear (no-memory) envelope detector. The interesting result is shown that the output rms bandwidth depends only on the input rms bandwidth and the nonlinear device and not on the shape of the input spectrum. As an illustrative example, it is shown that the rms bandwidth of the output of anuth-law envelope detector issqrt{nu/2}times the rms bandwidth of the input process. Some attention is given to the determination of higher moments of the output spectrum in terms of moments of the input spectrum.     

A low‐complexity MSK‐based M‐ary cyclic‐shift keying transceiver for direct sequence spread spectrum system over multipath fading channels

In this paper, a low‐complexity spread spectrum system with M‐ary cyclic‐shift keying (MCSK) symbol spreading is proposed. In addition, by using the minimum‐shift‐keying (MSK) as the chip‐level modulation, we obtain a high‐rate QPSK‐MCSK transceiver scheme which not only provides a constant‐envelop and continuous‐phase transmitted signal, but can also achieve a better performance than the conventional direct sequence spread spectrum (DSSS) system. At the transmitter, the data stream is first mapped into QPSK‐MCSK symbols in terms of orthogonal Gold code sequences, then followed by the cyclic prefix (CP) insertion for combating the interblock interference, and finally applying the MSK scheme to maintain the constant‐envelope property. The receiver first performs MSK demodulation, then CP removal, and finally the channel‐included MCSK despreading and symbol demapping. Furthermore, the single input single output (SISO) QPSK‐MCSK transceiver can be easily extended to the multiple input single output (MISO) case by incorporating the space–time block coding for high‐link quality. Simulation results show that the proposed SISO and MISO QPSK‐MCSK systems significantly outperform the conventional DSSS counterparts under the AWGN channel, and attain a more robust performance under the multipath fading channel. Copyright © 2011 John Wiley & Sons, Ltd.     

Evaluation of a Method for Interference Control in Analog FM Systems

We discuss a possible method for interference control in radio systems whose desired signal is analog FM. The method utilizes the fact that the desired signal has a nearly constant envelope; with interference present, the composite envelope becomes noisy. A controlling processor measures this additional envelope noise, and iteratively adjusts the complex combining gain of an auxiliary signal to minimize the interference. The expected residual interference remaining after minimization is proportional to the reciprocal of the square of the rms envelope fluctuation of the desired signal. This result was confirmed in a laboratory simulation of an intersecting radio route case using both large and small index FM. Beginning with signal-to-interference ratios of 30 to 40 dB, the controller increased these numbers to about 60 dB, the expected theoretical limit for a signal with 0.1 percent rms envelope fluctuation.     

Effects of Narrow-Band Filters on the Output Envelopes and Phases of Joint AM-FM Inputs: An Analytical Extension of the Bedrosian-Rice Formulation

The problem of determining the waveform distortion produced by a (symmetrical) narrow-band linear filter when an off-tune, simultaneously amplitude- and angle-modulated carrier is introduced, is analytically solved by an extension of the Bedrosian-Rice approach [1]. Here, both the instantaneous angle and envelope of the resulting narrowband output are determined. These results provide a basis for numerical calculations and extension to the more complex problem of interference effects produced by multiple inputs of the above type.     

基于窗函数的Chirp-UWB信号研究

与目前普遍研究的超宽带通信系统中所使用的高斯脉冲波形不同,线性Chirp信号具有良好的自相关性和高处理增益,能够更好地抵抗窄带干扰和多普勒频移。由于目前研究的线性Chirp信号普遍采用的方波包络,经过匹配滤波之后输出的sinc波形中,部分能量泄露到旁瓣中去,从而影响判决的精确度。选取了四种窗函数,经过窗函数处理之后的线性调频信号能有效地降低旁瓣的幅度,从而提高信号传输的能量利用率。通过仿真发现这种经过加窗处理之后的线性Chirp信号和方波包络的线性Chirp信号相比,在高斯噪声信道下具有更好的抗噪声性能。     

Spectrum efficiency of GMSK land mobile radio

Gaussian-filtered minimum-shift keying (GMSK) is a constant envelope and narrow-band modulation suitable for power- and band-limited digital radio communication. From the viewpoint of efficient spectrum use by land mobile radio, geographical reuse of cochannels as well as power spectrum compactness are desired. The output power spectrum of GMSK modulation can be made compact, at a sacrifice of co-channel interference protection. Parameters for optimizing GMSK are determined maintaining a compromise between co-channel reuse and power spectrum compactness.     

Hard-limiting of two signals in random noise

Two sinusoidal signals and Gaussian noise lying in a narrow band are passed through an ideal band-pass limiter that confines the output spectrum to the vicinity of the input frequencies. The output spectrum, consisting of both discrete and continuous components, is studied in terms of its corresponding autocorrelation function. The discrete output components are identified with the output signals and intermodulation products due to interference between the two input signals. The continuous part of the spectrum is associated with the output noise. The effects of limiting are expressed by ratios among the average powers of the output spectral components. Performance curves are given that show signal suppression, the ratio of output to input SNR's, and the relative strength of the intermodulation terms.     

Maximum Likelihood Receiver for Multiple Channel Transmission Systems

A maximum likelihood (ML) estimator for digital sequences disturbed by Gaussian noise, intersymbol interference (ISI) and interchannel interference (ICI) is derived. It is shown that the sampled outputs of the multiple matched filter (MMF) form a set of sufficient statistics for estimating the input vector sequence. Two ML vector sequence estimation algorithms are presented. One makes use of the sampled output data of the multiple whitened matched filter and is called the vector Viterbi algorithm. The other one is a modification of the vector Viterbi algorithm and uses directly the sampled output of the MMF. It appears that, under a certain condition, the error performance is asymptotically as good as if both ISI and ICI were absent.     

Experimental evaluation of postdetection diversity reception ofnarrow-band digital FM signals in Rayleigh fading

Postdetection diversity is attractive for narrowband digital FM signal reception because the cophasing function, which may be difficult to realize in a fast Rayleigh fading environment, is not required. The combining scheme evaluated here is to weight each frequency demodulator (FD) output in proportion to the νth power of the received signal envelope of that branch. Maximum diversity improvement can be obtained with ν=2 (this combiner is referred to as a postdetection maximal ratio chamber (MRC)). Experimental results are presented on postdetection diversity reception in the Gaussian minimum shift keying (GMSK) signal transmission system. Diversity combining and FD-decision algorithms (decision feedback equalizer (DFE) and maximum-likelihood sequence estimator (MLSE)) are performed by software on a computer using the data of the sampled FD output and received signal envelope obtained from a laboratory transmission system. It is shown that the MRC can attain about a 1-dB larger diversity gain than the selection combiner (SC) when two-branch diversity is used. The degradations of two-branch diversity improvement caused by the differences between demodulator sensitivities and between received signal envelope detector gains are evaluated     

A Digital Envelope Modulator for a WLAN OFDM Polar Transmitter in 90 nm CMOS

A digital envelope modulator as part of a polar transmitter architecture for the 802.11a/g WLAN OFDM standards is investigated. The digital envelope modulator is quite similar to a state-of-the-art DAC design, but now it has been optimized to deal with envelope signals. A thermometer-coded envelope DAC has been implemented in a 90 nm digital CMOS process. Measurements of a test chip show the digital envelope modulator to reach an OFDM output power of 5 dBm for 54 Mb/s using 64 QAM at 2.45 GHz and fulfilling EVM specifications and in-band spectral mask requirements using just 12.7 mW from a 1.2 V supply. Combining the digital envelope modulator with an off-chip power amplifier gives an output power of 20.4 dBm, while fulfilling EVM specifications and in-band spectral mask requirements. The output power of the presented envelope DAC can be increased in a re-design by scaling device sizes. The envelope DAC is a key component in a software-defined-radio transmitter.     

一种半集总微波带通滤波器的设计

本文设计了一种适用于阵列天线的带通滤波器,主要用于抑制杂波干扰。该滤波器以传统椭圆函数滤波器设计理论为基础,并对输入输出端口进行高低通包络匹配,从而解决了椭圆函数滤波器带外抑制平缓的问题 。为了满足滤波器设计指标的要求,电路采用半集总参数思路实现。文中给出了该滤波器的设计过程及实际测量结果。实测结果和仿真结果相符合,满足技术指标要求。     

Triangular quad-port multi-polarized UWB MIMO antenna with enhanced isolation using neutralization ring

In this study, a quad-port multi-polarized ultra-wideband (UWB) multiple input multiple output (MIMO) antenna system with a new isolation technique is designed for wireless devices. The antenna structure consists of four triangular monopole elements and neutralization ring (NR) structures. The monopoles are back-to-back positioned in symmetrical and orthogonal arrangement. Therefore, they radiate towards four directions without interference, and thus the diversity performance is improved. A novel NR is formed by combining a rectangular ring and a straight line to reduce the mutual coupling due to interoperation of the elements. Each triangular monopole is fed by 50 Ohm microstrip transmission line (MTL) with a thin strip line for ensuring impedance matching. Antenna performance in terms of impedance bandwidth, current distribution, radiation pattern, peak gain and envelope correlation coefficient (ECC) is also investigated. The MIMO antenna system has 3.1–17.3 GHz impedance bandwidth, 1–5 dBi peak gain variation, less than 0.1 ECC. The results indicate that the proposed antenna has the characteristics of larger UWB bandwidth, high isolation by the NR structure, multi-polarization, uniform gain and quasi-omnidirectional pattern.     

SIR analysis and interference cancellation in uplink OFDMA with large carrier frequency/timing offsets

In uplink orthogonal frequency division multiple access (OFDMA), large timing offsets (TO) and/or carrier frequency offsets (CFO) of other users with respect to a desired user can cause significant multiuser interference (MUI). In this letter, we analytically characterize the degradation in the average output signal-to-interference ratio (SIR) due to the combined effect of both TOs as well as CFOs in uplink OFDMA. Specifically, we derive closed-form expressions for the average SIR at the DFT output in the presence of large CFOs and TOs. The analytical expressions derived for the signal and various interference terms at the DFT output are used to devise an interference cancelling receiver to mitigate the effect of CFO/TOinduced interferences.