Blind carrier phase tracking with guaranteed global convergence

Conventional blind carrier recovery algorithms have been observed to show unstable behaviors for large constellation modulation schemes such as 64-QAM or 256-QAM. We propose a new carrier tracking approach that has guaranteed global convergence. First, we show that the carrier tracking problem is equivalent to a blind source separation problem, which involves the separation of a linear unitary mixture of two independent components that are the real and imaginary parts of the emitted signal. Then, by using a blind source separation procedure, we derive a new and robust carrier tracking algorithm with guaranteed global convergence. Some numerical simulations are provided to illustrate the effectiveness of the proposed method     

APSK长突发信号的动态载波相位跟踪

APSK已被用于宽带数字卫星通信,在采用APSK长突发的卫星通信中,需要对一帧内的载波相位动态变化进行跟踪。针对粗载波同步和符号同步完成后的长突发APSK调制信号,提出一种新的载波跟踪方案,该方案采用一种基于星座分割的NDA鉴相算法,使用两个二阶锁相环,并借助于一个很短的独特码解相位模糊,可在很高的数据传输效率下,克服一般闭环法的捕获时间问题,实现对整帧信号载波相位的顺利跟踪。     

Space telemetry degradation due to Manchester data asymmetryinduced carrier tracking phase error

The author analyzes the deleterious effects that the Manchester (or Bi-φ) data asymmetry has on the performance of phase-modulated residual carrier communication systems. Expressions for the power spectral density of an asymmetric Manchester data stream, the interference-to-carrier signal power ratio (I/C), and the error probability performance are derived. Since data asymmetry can cause undesired spectral components at the carrier frequency, the I/C ratio is given as a function of both the data asymmetry and the telemetry modulation index. Further, the data asymmetry and asymmetry-induced carrier tracking loop and the system bit-error rate to various parameters of the models are presented     

Reconfigurable multilevel phase holograms for optical switches

A way of dynamically encoding polarization-insensitive multilevel phase holograms using nematic liquid crystals is presented. The method, using a quarter wave plate and a mirror, allows the optical efficiency of a free space single-mode fiber-to-fiber switch to be greatly enhanced. The validity of the approach has been verified experimentally by observing the power diffracted in the ±1 orders of a nematic liquid crystal grating as a function of input polarization and applied voltage     

Mobile GPS carrier phase tracking using a novel intelligent dual‐loop receiver

Carrier phase information is necessary for accurate measurements in global positioning system (GPS) applications. This paper presents a novel intelligent GPS carrier tracking loop with variable‐bandwidth characteristics for fast acquisition and better tracking capability in the presence of dynamic environments. Our dual‐loop receiver is composed of a frequency‐locked loop‐assisted phase‐locked loop structure, the fuzzy controllers (FCs), and the ATAN discriminator functions. The soft‐computing FCs provide the time‐varying loop gains to perform accurate and reliable control of the dual‐loop paradigm. Once the phase dynamic errors become large under kinematic conditions, the fuzzy loop gains increase adaptively and achieve rapid acquisition. On the other hand, when the tracking errors approach zero in the steady state, the loop gains decrease and the corresponding dual‐loop receiver returns to a narrowband system. Four types of carrier phase signals, i.e. phase offset, decaying sinusoidal phase jitter, frequency offset, and frequency ramp offset, are considered to emulate realistic mobile circumstances. Simulation results show that our proposed receiver does achieve a superior performance over conventional tracking loops in terms of faster settling time and wider acquisition range while preventing the occurrence of cycle slips. Copyright © 2008 John Wiley & Sons, Ltd.     

Recursive computations for the optimal tracking of time-varying parameters (Corresp.)

Recursive relations are given for updating the conditional densityp(theta_{k} | X_{k-1}, cdots X_{1})(also forp(theta_{k} | X_{k}, cdots, X_{1})), wheretheta_{k}is a parameter of the density ofX_{k}. The observationsX_{1}, X_{2}, cdotsare assumed to be conditionally independent (i.e., for known parameters), and the sequence of time-varying parameterstheta_{1}, theta_{2}, cdotsconstitutes a Markov-M sequence. The result requires the storage of an intermediate function of(theta_{k-1}, cdots , theta_{k-M}).     

模块化多电平静止无功补偿器控制策略研究

随着多电平逆变器在电力系统无功功率补偿领域的广泛应用,提出了一种基于模块化多电平( MMC)技术的新型静止无功补偿器( STATCOM)的拓扑结构。该拓扑结构具有模块化程度高、可靠性好、便于维护及容量拓展等特点,是一种极具发展潜力的拓扑结构。首先对MMC-STATCOM的工作原理和数学模型进行了分析,提出了无功功率解耦控制策略以及提出了一种新的控制子模块电容电压平衡的控制算法。仿真和测试结果均表明MMC-STATCOM具有补偿效果好,动态响应速度快等优点,是一种具有工程应用价值的大容量STATCOM主电路拓扑。     

Blind carrier phase acquisition for QAM constellations

A constant need for ever-increasing throughputs through fixed bandwidths, fueled by several high-speed applications (such as digital TV), has pushed system designers toward more throughput-efficient modulation schemes. Because of their relatively good performance, large quadrature amplitude modulation (QAM) constellations are being used in many of these applications. One of the problems associated with the use of large QAM constellations is that of carrier acquisition, which, for efficiency reasons, must often be done without the use of a preamble. The problem is further complicated for cross constellations, for which the high signal-to-noise ratio (SNR) corner points used by some simple carrier phase estimators are not available. We derive simple algorithms for carrier phase acquisition that can be used for both square and cross constellations, and compare their performance to those of the maximum-likelihood (ML), the fourth-power estimator, and a modified fourth-power estimator, obtained by considering a reduced constellation. The introduced algorithms convert the problem of carrier phase estimation into one of estimating the mode of an underlying distribution. An expression for this underlying distribution is also obtained. The results obtained indicate that the introduced algorithms significantly outperform the fourth-power estimator for moderate to high SNRs, especially when cross constellations are used     

多级石英延迟器件相位延迟差研究

利用光在双折射晶体中传播遵循的规律,给出了斜入射光束在两个特殊截面(光轴平行于入射面和光轴垂直于入射面)上的相位延迟的计算公式和小角入射的近似处理。从理论上定量给出方位变化与延迟量变化的关系,从而为延迟器件的调整和正确使用提供理论依据。     

基于反推的永磁同步电动机伺服系统的位置跟踪控制

永磁同步电动机工作性能优越，在当前交流伺服系统的驱动控制当中起着越来越重要的作用。为了实现永磁同步电动机的精确位置跟踪，把一种新颖非线性控制方法Backstepping应用于永磁同步电动机伺服系统控制器的设计。Backstepping控制器的设计以保证系统的全局一致渐近稳定为原则，因此该控制器不但可以保证系统的全局一致渐近稳定，而且系统具有快速跟踪，定位精确的特点。系统的设计能够有效降低转矩变化对位置跟踪性能的影响。最后通过Matlab仿真验证了系统设计的有效性和可行性。     

A phase tracking system for three phase utility interface inverters

The analysis and design of the phase-locked loop (PLL) system is presented for the phase tracking system of the three phase utility interface inverters. The dynamic behavior of the closed loop PLL system is investigated in both continuous and discrete-time domains, and the optimization method is considered for the second order PLL system. In particular, the performance of the three phase PLL system is analyzed in the distorted utility conditions such as the phase unbalancing, harmonics, and offset caused by the nonlinear load conditions and measurement errors. The tracking errors under these distorted utility conditions are also derived. The phase tracking system is implemented in a digital manner using a digital signal processor (DSP) to verify the analytic results. The design considerations for the phase tracking system are deduced from the analytic and experimental results     

GPS接收机载波跟踪环设计与分析

针对GPS接收机载波跟踪环环宽与跟踪的动态性能问题,在分析影响GPS信号动态性能的主要参数热噪声、晶振Allan相位噪声、晶振振动相位噪声和动态应力的基础上,通过对不同阶数的锁相环、锁频环跟踪门限分析与仿真,主要解决了如何设计GPS接收机的载波跟踪环路的带宽,并使系统性能达到最佳的问题,即使用环宽为18 Hz的二阶锁相环辅助环宽为10 Hz的三阶锁频环可以跟踪动态范围小于10 g、100 g/s的高动态信号。     

Multiple-phase codes for detection without carrier phase reference

We consider the construction and analysis of linear block codes for M-ary phase-shift keying that can be decoded without carrier phase synchronization. Under these circumstances, the function that has a significant impact on performance is the noncoherent distance, analogous to the Euclidean distance for the coherent case. The major difficulty in constructing and analyzing such codes lies in the fact that the noncoherent distance is not a true metric. For this reason, prior work mainly relies on numerical approaches to search for good codes and to determine the corresponding minimum noncoherent distance. We first present a theorem that links the noncoherent distance with the Euclidean and Lee (1958) distances. This theorem allows us to construct good codes and determine their minimum noncoherent distances analytically. Based on this theorem, we classify the codes whose duals consist of a cyclic group. These codes are of minimum redundancy. We further investigate codes with the flavor of Hamming and shortened Hamming codes. Many of these new codes provide significantly larger coding gains than previously known codes. Linear codes derived from code-division multiple-access (CDMA) sequences are considered as well. These codes in general provide rather large coding gains. Finally, an algorithm is introduced that can be appended to any suboptimal decoding technique to enhance the performance     

Channel coding with multilevel/phase signals

A coding technique is described which improves error performance of synchronous data links without sacrificing data rate or requiring more bandwidth. This is achieved by channel coding with expanded sets of multilevel/phase signals in a manner which increases free Euclidean distance. Soft maximum--likelihood (ML) decoding using the Viterbi algorithm is assumed. Following a discussion of channel capacity, simple hand-designed trellis codes are presented for 8 phase-shift keying (PSK) and 16 quadrature amplitude-shift keying (QASK) modulation. These simple codes achieve coding gains in the order of 3-4 dB. It is then shown that the codes can be interpreted as binary convolutional codes with a mapping of coded bits into channel signals, which we call "mapping by set partitioning." Based on a new distance measure between binary code sequences which efficiently lower-bounds the Euclidean distance between the corresponding channel signal sequences, a search procedure for more powerful codes is developed. Codes with coding gains up to 6 dB are obtained for a variety of multilevel/phase modulation schemes. Simulation results are presented and an example of carrier-phase tracking is discussed.     

一种改进的高动态GPS载波组合跟踪环路算法

在高动态的接收环境下,GPS接收机接收信号载频上会产生很大的多普勒频移及其变化率,传统的GPS载波跟踪环无法保证可靠的跟踪。在综合分析了常规跟踪方案的利弊后,提出一种新的基于四相鉴频（FQFD）牵引的二阶叉积自动频率控制环（CPAFC）辅助三阶锁相环（PLL）高动态跟踪环路算法。通过美国喷气推进实验室（JPL）高动态载体模型测试表明,该算法在高动态环境下不仅能快速牵入和锁定载波信号,而且在高达100g/s的加加速度作用过程中能持续、精确跟踪,实现导航电文的正常解调。     

一种基于判决反馈的OFDM系统载波频率跟踪算法

研究了多径信道下OFDM系统的一种新的载波频率跟踪算法，这种算法以判决反馈和接收端的时域信号重构为基础。推导了估计结果的精确解，比较了使用原估计结果和新的估计结果进行频偏补偿时系统跟踪性能的不同。通过对算法的仔细分析，发现除了通常的加性噪声外，信道估计误差、子载波数目和子载波的调制方式也影响频偏的估计结果和跟踪范围，而且子载波的数目和调制方式是决定性的因素。这种频率跟踪方法的优点是即使在很低的信噪比下仍然能获得高的跟踪精度，且实现相对简单。     

Recursive expectation-maximization (EM) algorithms for time-varyingparameters with applications to multiple target tracking

We investigate the application of expectation maximization (EM) algorithms to the classical problem of multiple target tracking (MTT) for a known number of targets. Conventional algorithms, which deal with this problem, have a computational complexity that depends exponentially on the number of targets, and usually divide the problem into a localization stage and a tracking stage. The new algorithms achieve a linear dependency and integrate these two stages. Three optimization criteria are proposed, using deterministic and stochastic dynamic models for the targets     

Adaptive iterative detection for phase tracking in turbo-codedsystems

The problem of performing iterative detection (ID)-a technique originally introduced for the decoding of turbo codes-for systems having parametric uncertainty has received relatively little attention in the open literature. In this paper, the problem of adaptive ID (AID) for serial and parallel concatenated convolutional codes (SCCCs and PCCCs or turbo codes) in the presence of carrier-phase uncertainty is examined. Based on the theoretical framework of Anastasopoulos and Chugg, (see Proc. Int. Conf. Communications, p.177-181, 1999). and Colavolpe, Ferrari and Raheli (see IEEE Trans. Commun., vol.48, p.1488-98, 2000), adaptive soft inverse (ASI) algorithms are developed for two commonly used blocks in turbo codes, leading to the adaptive soft-input soft-output (A-SISO) and the adaptive soft demodulator (A-SODEM) algorithms. Based on these algorithms, practical AID receivers are presented. Several design options are proposed and compared and the impact of parametric uncertainty on previously established results for iterative detection with perfect channel state information (CSI) is assessed     

A symmetric carrier technique of CRPWM for voltage balance method of flying-capacitor multilevel inverter

This paper presents a simple carrier symmetric method for the voltage balance of flying capacitors in flying-capacitor multilevel inverters. The carrier-redistribution pulsewidth-modulation (CRPWM) method was reported as a solution for the voltage balance but it has a drawback at the transition of voltage level. To achieve the voltage balance of flying capacitors, the utilization of each carrier must be balanced during a half-cycle of the switching period such as phase-shifted PWM. However, the CRPWM method causes the fluctuation of flying-capacitor voltages because the balanced utilization of carriers is not achieved. Moreover, it does not consider that the load current change has an influence on flying-capacitor voltages by assuming that the current flows into the load. Therefore, the charging and discharging quantities of flying-capacitor voltages do not become zero during the switching period. To overcome the drawbacks of CRPWM, it is modified by the technique where carriers of each band are disposed of symmetrically at every fundamental period. Firstly, the CRPWM method is reviewed and the theory on voltage balance of flying capacitors is analyzed. The proposed method is introduced and is verified through simulation and experimental results.     

The synchronous oscillator: a synchronization and tracking network

The synchronous oscillator (SO) is a free-running oscillator which oscillates at its natural frequency in the absence of an externally applied signal. In the presence of a signal, the oscillator synchronizes with and tracks the input waveform with an acquisition time inversely proportional to the tracking bandwidth. The SO possesses a constant output signal amplitude in the tracking region and an adaptive tracking bandwidth proportional to the input signal level. The authors present the theory and experimental characterization of SOs in terms of selectivity, noise rejection, carrier-to-noise improvement, tracking range, and acquisition time. A specific application is described for SO carrier and clock recovery networks in 60- and 120-Mb/s QPSK modem with bit-error-rate (BER) performance approaching that of hard-wired connection.