Protection of PSK Communication Systems with Adaptive Arrays

The performance of binary phase-shift-keyed (BPSK), binarydifferential phase-shift-keyed (DPSK), and quadrature phase-shift-keyed(QPSK) communication systems that use adaptive arrayantennas for interference rejection is examined. The case where thedesired signal is corrupted by continuous wave (CW) interference isspecifically addressed. The performance of the adaptive array andthe ideal BPSK, DPSK, and QPSK detectors are evaluated first andthe results of these calculations are combined to determine theoverall system performance. The bit-error probability at the systemoutput is used as the performance measure. Several examples arepresented which illustrate the effects of signal powers, arrivalangles, frequencies, and the array input bandwidth.     

Phase modulated DGPS transmitter implemented with a clamped-mode resonant converter

A clamped-mode resonant converter (CMRC) is proposed to be used as a transmitter which broadcasts correction signals in a differential Global Positioning System (DGPS). The digital information of the DGPS modulates the carrier with different modulation methods minimum shift keying (MSK) (recommended for the marine radiobeacon band), stepped binary phase shift keying (S-BPSK) and BPSK. The first two methods allow keeping the converter's operation in soft switching mode. Extensive trials under impedance mismatch and modulation conditions confirm that the soft switching mode is preserved.     

GNSS干扰信号检测方法研究

研究了GNSS导航接收机在干扰源条件下的干扰检测和识别技术。除常见的卫星干扰如脉冲干扰、扫频干扰、BPSK干扰、宽带高斯白噪声干扰外,还添加了QPSK和8PSK干扰进行建模分析,并提取了常见的特征参数,如信号3dB带宽和频谱峰度等。通过研究,高阶累积量被提取作为MPSK干扰类内识别的特征参数。研究了基于决策树和BP神经网络等分类器算法的干扰盲识别,并分析比较了这些分类算法的识别准确率,为抗干扰领域的研究提供了重要参考。     

基于数字高速数据解调的Trellis-Coded MPSK与载波相位噪声

本文基于一种数字解调系统分析了在AWGN信道中载波相位噪声对Trellis-Coded MPSK的影响。同时利用存在载波相位噪声条件下的误码率上界公式，运用仿真工具simulink对未编码情况下的QPSK与Trellis-Coded MPSK及级联卷积编码情况下的QPSK与Trellis-Coded MPSK进行了蒙特卡罗仿真。分析结果表明：TCM-8PSK具有较强的载波相位噪声抑制能力。该结果对于进一步研究TCM-8PSK在卫星数传系统中的应用具有重要的参考价值。     

MSK and Offset QPSK Modulation with Bandlimiting Filters

It is considered by some that minimum shift keying (MSK) is spectrally more efficient than quaternary phase-shift keying/offset quadrature phase-shift keying (QPSK/OQPSK). An analytical method is presented here for determining the detection efficiencies of MSK and QPSK/OQPSK when the constant-envelope signal is passed through a set of filters and when the resulting signal is corrupted by Gaussian noise. The detection efficiency of MSK is compared with that of QPSK/OQPSK when a four-pole Butterworth filter is used as a transmit filter and for two different receive filter functions. When the two-sided 3-dB bandwidth of the transmit filter is between approximately 1.00/T and 1.50/T, it is shown that the detection efficiency of MSK is not substantially different from that of QPSK/OQPSK. For more severe bandlimiting of the signal, the performance of MSK is shown to be inferior to that of QPSK/OQPSK. It is, therefore, concluded that MSK does not have significantly better detection efficiency when the effect of bandlimiting filters is taken into account.     

Carrier-Tracking Loop Performance for Quaternary and Binary PSK Signals

By expressing the open-loop response voltage as a Fourier series in terms of the phase-tracking error and then utilizing a very useful mean-value expression, we assess the performance of loops suited to recovering the carrier of four-phase (quaternary) and two-phase (binary) phase-shift-keyed (QPSK and BPSK) signals. At high signal to noise ratios (SNRs) they perform comparably, but at low SNRs the former's performance deteriorates much more rapidly. The loop's ability to maintain the carrier frequency despite the noise accompanying the PSK signal is measured by the mean and the variance of the oscillator's control voltage. In particular, Spilker's loop for QPSK and the Costas loop for BPSK signals are discussed.     

Intersymbol and CW Interference in QPSK, OQPSK, and MSK Hard-Limiting Satellite Systems

A new equivalent model for deriving the bit error rate (BER) of quadrature phase-shift keying (QPSK), offset QPSK (OQPSK), and minimum shift keying (MSK) signals transmitted over hard-limited channels in the presence of up-link intersymbol interference (ISI) and CW interference (CWI) is introduced. In the equivalent model the up-link and down-link are interchanged in order to avoid the complicated expectation due to the up-link ISI at the hard-limiter output. The analysis is based on the moment technique and the Gram-Charlier expansion. Numerical results of the BER show that the large bandwidth-symbol time product (BT) or the existence of CWI makes MSK preferable compared with QPSK or OQPSK.     

Lock threshold deterioration induced by antenna vibration and signal coupling effects in hypersonic vehicle carrier tracking system of Ka band

The envelope of a hypersonic vehicle is affected by severe fluctuating pressure, which causes the airborne antenna to vibrate slightly. This vibration mixes with the transmitted signals and thus introduces additional multiplicative phase noise. Antenna vibration and signal coupling effects as well as their influence on the lock threshold of the hypersonic vehicle carrier tracking system of the Ka band are investigated in this study. A vibration model is initially established to obtain phase noise in consideration of the inherent relationship between vibration displacement and electromagnetic wavelength. An analytical model of the Phase-Locked Loop(PLL), which is widely used in carrier tracking systems, is established. The coupling effects on carrier tracking performance are investigated and quantitatively analyzed by imposing the multiplicative phase noise on the PLL model. Simulation results show that the phase noise presents a Gaussian distribution and is similar to vibration displacement variation. A large standard deviation in vibration displacement exerts a significant effect on the lock threshold. A critical standard deviation is observed in the PLL of Binary Phase Shift Keying(BPSK) and Quadrature Phase Shift Keying(QPSK) signals. The effect on QPSK signals is more severe than that on BPSK signals. The maximum tolerable standard deviations normalized by the wavelength of the carrier are 0.04 and 0.02 for BPSK and QPSK signals,respectively. With these critical standard deviations, lock thresholds are increased from à12 andà4 d B to 3 and à2 d B, respectively.     

Imperfect Carrier Recovery Effect on Filtered PSK Signals

Coherent demodulation of a PSK signal requires the generation of a local carrier phase reference. Methods are given to determine the detection loss caused by noisy phase recovery and its use in the coherent detection of filtered BPSK and QPSK signals. It is assumed that the phase noise can have a static part and a random component with a Tikhonov-type distribution. The static part is mostly due to offset frequency tracking of the PLL used to recover the carrier, while the random component is due to thermal noise present in the carrier recovery loop and is also due to the random nature of the phase modulation. It is shown that the probability of error of BPSK and QPSK can be expressed as a finite sum of a set of strictly alternating converging series when the number of ISI terms is finite. Upper and lower bounds on the probability of error have been derived when this number becomes infinite and we show how this error rate can be computed with any desired accuracy. Numerical results are presented for various values of static error and phase noise variance when the transmit and receive filters are 4-pole Butterworth filters. For filtered PSK signals and for a bit error rate of 10-6, our results show that the additional degradation in presentday receiver systems due to imperfect carrier recovery can be less than 0.1 dB for BPSK and less than 1 dB for QPSK.     

Digital data over video channels: Techniques for Spacelab

Various techniques for transmitting digital data over a composite video channel are examined, with a view to transmitting data from experiments on the Space Shuttle orbiter. PSK (phase-shift keying), MPSK (m-ary PSK), or PAM (pulse-amplitude modulation), which can be transmitted on visible lines of a frame, unassigned lines of the VBI (vertical blanking interval), or during the HBI (horizontal blanking interval), are all found to be attractive under the proper conditions. However, PAM on visible lines or during the VBI should be relatively easy to implement, provide adequate average data rates, and give acceptable BERs (bit error rates)     

Techniques for transmitting digital data on the spacelab's analogvideo channel

A study was made of various techniques for transmitting digital data over a composite video channel, with data from experiments on the Space Shuttle Orbiter in mind. Broadcast television telecommunications schemes and other techniques described in the literature were reviewed and compared. PSK (phase shift keying) MPSK (M-ary PSK), and or PAM (pulse amplitude modulation), which can be transmitted on visible lines of a frame, unassigned lines of the VBI (vertical blanking interval), or during the HBI (horizontal blanking interval), were all judged attractive under the proper conditions. However, PAM on visible lines or during the VBI should be relatively easy to implement, provide adequate average data rates, and give acceptable BERs (bit error rates)     

基于UKF准开环结构的高动态载波跟踪环路

 对高动态环境下的全球卫星导航系统（GNSS）载波信号跟踪方法进行了研究。在分析高动态载波信号模型的基础上,提出了一种基于无迹卡尔曼滤波（UKF）的准开环载波跟踪方法。此方法能够消除导航数据二进制相移键控(BPSK)调制的影响,并采用四维UKF相位估计模型提高跟踪精度,同时对估计值进行补偿以减少滤波器的滞后性。通过模拟接收机的高动态运动轨迹,从跟踪误差、跟踪结果和补偿效果3个方面,与基于卡尔曼滤波（KF）的锁频环(FLL)辅助锁相环(PLL)结构的传统跟踪方法进行比较,结果表明基于UKF的准开环跟踪方法能够有效地完成高动态环境下的载波跟踪。     

Probability of error for BPSK modulation from electrostaticinterference [in orbital situation]

In an orbital situation any spacecraft is bombarded by charged particles that span a broad range of energies. Some of the particles may be trapped within the materials of the spacecraft. Recent data indicates that an S-band phased-array antenna on a spacecraft may experience electrostatic discharges from such ion deposition at the elements of the array. These discharges may induce RF interference of sufficient magnitude to degrade transponder performance. This issue is addressed by considering the degradation to a binary phase shift keying (BPSK) signal. A simple model for the electrostatic phenomenon is described, and error probabilities are evaluated. The discharges and induced pulse rates are shown to be well below the interference level     

Multi-objective approach in GNSS code discriminator design

In spread spectrum ranging system receivers such as the Global Navigation Satellite System (GNSS) receivers, a discriminator is used in the code tracking loop to provide an error signal for the tracking of incoming signals. Typically, the discriminator manipulates several correlator outputs to form the correction signal. A multi-objective approach is adopted here to design the coefficients associated with a multi-correlator-based discriminator to lead to a better performance tradeoff in large tracking range, acceptable multipath-induced bias, high sensitivity, free of ambiguity, and small variance. It is shown that the multiple-objective problem can be tackled via a quadratic/linear programming method, rendering the optimal coefficient vector for the implementation of the discriminator. In addition, as the discriminator design is often subject to conflicting requirements, it is shown that the proposed design approach is capable of establishing bounds on achievable performance. Examples with respect to BPSK (binary phase-shift keying) NRZ (nonreturn-to-zero), and BOC (binary-offset carrier) signals are given to illustrate the design approach.     

一种基于证据距离的多分类器差异性度量

 多分类器系统因其能够显著提升分类精度而引发了广泛关注。多分类器系统中各子分类器间的差异性是提升融合分类精度的先决条件。提出了一种基于证据距离的分类器系统差异性度量,同时基于该度量提出一种多分类器系统构造方法。综合了既有差异性度量、所提新差异性度量以及在训练样本集上的分类性能等多个指标,实现了多分类器系统的有效构造。实验结果表明,所提差异性度量及多分类器系统构造方法是合理的,能有效提升融合分类精度。     

Classification of radar targets using synthetic neural networks

Radar target classification performance of neural networks is evaluated. Time-domain and frequency-domain target features are considered. The sensitivity of the neural network algorithm to changes in network topology and training noise level is examined. The problem of classifying radar targets at unknown aspect angles is considered. The performance of the neural network algorithms is compared with that of decision-theoretic classifiers. Neural networks can be effectively used as radar target classification algorithms with an expected performance within 10 dB (worst case) of the optimum classifier     

一种时间传递系统中调制器时延的数字标定算法

针对传统示波器观察法测量BPSK（Binary phase shift keying,二进制相移键控）调制器时延时存在整码元模糊、噪声敏感、载波初相要求苛刻及标定精度低的缺点,利用软件无线电的相关处理技术,提出一种精密的BPSK调制器时延标定算法.通过高速数字示波器对BPSK调制器的输入基带信号和输出载波调制信号进行双通道同步过采样,对输出信号与输入信号采样值进行循环相关,根据相关峰值对应的样本点序号以及连接电缆的校准时延,计算得到BPSK调制器时延.仿真和试验验证表明：提出的算法不受载波初始相位影响,时延标定上限可达1个伪随机码周期,而且低载噪比情况下也能得到准确结果.数字示波器的通道采样率为10 GSa/s时,采用提出的算法进行BPSK调制器时延标定,标定结果的不确定度可以达到0.2 ns.     

PSK communications systems using fully saturated power amplifiers

Quasiconstant envelope phase-shift keying (PSK) is analyzed to assess its ability to overcome nonlinearities caused by fully saturated RF power amplifiers in communications systems. These modulations can achieve bit error rate (BER) performance comparable to linear BPSK in additive white Gaussian noise (AWGN) channel. Quasiconstant envelope offset quadrature PSK (OQPSK) is presented as a design example. At a BER = 10/sup -5/, the SNR degradation caused by fully saturated power amplifiers is 0.1 dB. The simulated BER matches analytically derived results. For a communications system employing the quasiconstant envelope OQPSK and a rate 1/2 convolutional code with K = 7, the demodulation performance is degraded by 0.25 dB at a BER = 10/sup -5/ when a fully saturated power amplifier is employed.     

Automatic target classification of slow moving ground targets in clutter

A new approach is proposed which will allow air-to-ground target classification of slow moving vehicles in clutter. A wideband space-time adaptive (STAP) filter architecture, based on subbanding, is developed and coupled with a one dimensional template-based minimum mean squared error (MMSE) classifier. The performance of this STAP/ATC (automatic target classification) algorithm is quantified using an extensive simulation. The level of residual clutter afforded by various filter configurations and the associated incremental improvement in ATC performance is quantified, revealing the potential for realizable hardware and software implementations to achieve acceptable ATC performance.     

一种基于指数损失函数的多类分类AdaBoost算法及其应用

 提出一种新的多类分类AdaBoost算法——使用多类分类指数损失函数的前向逐步叠加模型FSAMME（forward stagewise additive modeling using a multi class exponential loss function）。该算法是基于原始的两类分类AdaBoost算法归结为使用两类分类指数损失函数的前向逐步叠加模型的统计学观点,将两类分类的前向逐步叠加模型自然扩展到多类分类情况下得到的,并采用多类指数损失函数和前向逐步叠加模型对FSAMME进行了详细的理论证明。该算法大大降低对弱分类器的精度要求,只需每个弱分类器的精度比随机猜测好;算法简单明了,不用把多类问题转化为多个两类问题,而是直接求解多类分类问题,大大减小计算复杂度和计算量。通过对基准数据库的测试分类及航空发动机故障样本的诊断,结果表明:FSAMME算法一方面可达到较高的分类诊断准确率,其准确率明显高于AdaBoost.M1,略高于AdaBoost.MH;另一方面可大大减小计算成本,满足在线快速分类诊断的要求。