Singer模型在周跳探测中的应用

假设三参数的载波相位多项式,同时利用预报星历数据进行后处理,代估计量假设为Singer模型,采用kalman滤波算法对载波相位进行计算,得到计算与观测载波相位的差值,从而可探测是否发生了周跳。经过仿真实验,表明这种新的周跳检测方法可以很好地检测出周跳,实用性很高。     

有源光纤环路脉冲复制特性的研究

理论分析和实验验证了一种提高有源光纤环路脉冲复制性能的解决方案。首先,经过理论分析推导出决定脉冲复制性能的主要参数是光放大器增益的动态特性。其次,理论分析得出通过改变环路衰减,利用光纤环路内的放大自发辐射噪声光信号调整光放大器工作状态,减小光放大器增益的动态范围。最后,通过实验测量复制脉冲序列波形,验证了光放大器工作在深度饱和状态可以提高有源光纤环路脉冲复制的性能。并且通过实验测量光纤环路光谱,进一步分析证明光放大器饱和状态是指相应频带的饱和。因此使用光滤波器对光纤环路频带进行限制是非常必要的。     

Noncoherent data transition tracking loops for symbol synchronization in digital communication receivers

Starting with the maximum a posteriori (MAP)estimation approach, this paper derives the optimum (in the MAP estimation sense) means for performing symbol-timing recovery in the absence of carrier-phase information (i.e., prior to carrier-phase recovery). Specifically, we examine the necessary modification of a well-known form of coherent symbol synchronizer,namely, the data transition tracking loop (DTTL), to allow its operation in the absence of carrier-phase information, i.e., as a so-called noncoherent symbol sync loop. By employing such a noncoherent scheme, one can eliminate the need for iteration between the carrier and symbol sync functions,as typically takes place in receivers that more commonly perform carrier tracking and acquisition prior to symbol timing. The performance of both the linear and nonlinear versions of this noncoherent DTTL is obtained by a combination of analysis and simulation, and compared with that of the corresponding coherent DTTLs.     

关于通信时间同步网技术性能的探讨

针对通信时间同步网的关键性能指标,对比国内外相关技术标准的差异,并结合通信技术和业务发展对于同步性能的需求,探讨时间同步网端到端同步性能指标分配模型、时间偏差值限定等。     

TD-SCDMA直放站下行同步算法性能研究

文章首先介绍了下行同步精度及稳定度在时分同步码分多址(TD-SCDMA)直放站应用中的重要作用,然后结合ADS(Advanced Design System)对特征窗捕获匹配和相关解调两种同步算法的仿真结果,从算法原理上比较了这两种同步算法的抗干扰性能.最后根据仿真统计结果结合直放站实际应用状况分析了两种同步算法的优缺点和适用环境,并根据实际应用中的问题提出了一些改良意见.     

Acquisition performance of various QPSK carrier tracking loops

The frequency and phase acquisition performance of three quadrature phase shift keying (QPSK) carrier tracking loops, the MAP estimation loop, the Costas crossover loop, and the generalized Costas loop, is described. Acquisition time and probability of acquisition as a function of both loop signal-to-noise ratio and frequency offset to loop bandwidth ratio are obtained via computer simulations for type II and III loops. It is shown that the MAP loop, which results in the smallest squaring loss for all signal-to-noise ratios, is sometimes outperformed by the other two loops in terms of acquisition time and acquisition probability     

Studies on the performance of phase-locked loops incorporating modified loop filters

The behaviour of a phase-locked loop (PLL) is highly dependent on the structure of the loop filter. In the present paper, the filter structure has been modified by incorporating a high-pass filter connected in parallel to the conventional low-pass filter. Numerical results show that a proper choice of design parameters of the filters can enhance the transient response of a PLL as well as improve its noise rejection capability in some specific cases. The filter modification algorithm has been verified by means of a software experiment using MAT-LAB, and through a hardware experiment.     

The impact of synchronization on the performance of FDL buffers

Circumventing the speed bottleneck of electronic switching, novel switching approaches like optical burst switching (OBS) and optical packet switching (OPS) handle the switching of bursts (or packets) in backbone nodes optically, and include a set of fiber delay lines (FDLs) for optical buffering. While previous work acknowledges the performance difference between optical FDL buffers and electronic RAM buffers, the important role of synchronization herein has received little attention to date.     

矢量跟踪算法快速重跟性能分析

当卫星导航信号受到一段时间干扰或遮蔽时,信号载噪比下降,传统跟踪环路失锁。信号恢复时,针对传统跟踪环路不能及时重新跟踪问题,应用矢量跟踪算法,进行跟踪。分析了在真实GPS数据加上仿真噪声之后矢量/频率锁定环路（VDFLL）的性能以及与传统环路进行对比,试验证明矢量跟踪具有快速重跟性能。     

On the performance limits of data-aided synchronization

This paper addresses data-aided (DA) synchronization, in which the reference parameter acquisition is aided by a training sequence known to the receiver. The Cramer-Rao lower bound (CRB) for the DA timing and/or carrier phase recovery is presented. For DA parameter estimation, the CRB typically varies with the training sequence. This indicates that different training sequences offer fundamentally different performance. In the literature, the widely cited closed-form CRB for timing and carrier phase recovery was derived under the assumption that the training sequence is independent and identically distributed (i.i.d.) and sufficiently long. We derive a closed-form CRB for timing and carrier phase recovery with respect to an arbitrary training sequence and pulse shaping function for the over and under sampling cases. It turns out that the CRB is a weighted summation of the aperiodic correlation of the training sequence and the weighting factor is determined by the pulse shaping filter. Therefore, this paper reveals the fundamental link between a training sequence and its corresponding performance limit.     

联合多普勒及MW周跳探测和修复方法

导航定位中针对双频码相组合法(MW)无法探测L1和L2载波同一历元发生相同周跳,以及周跳探测后不能实现频率间周跳分离的情况,提出了一种联合多普勒及MW组合法的周跳探测改进方法。利用多普勒积分可对单频点进行周跳检测和修复的特性,将传统MW组合法与多普勒积分法相结合,建立改进模型,从而计算并分离出L1和L2载波相位产生的周跳。用实测数据进行验证和分析,对比了3种不同情况下改进方法的检测效果,实验表明新算法能精确探测和分离出L1和L2载波相位中的周跳组合,可以准确探测周跳发生位置及周跳数值,并且能够探测和修复1周以上的周跳,有效提高了MW组合算法探测与修复周跳的准确性和可靠性。     

Impact of synchronization on performance of enhancedarray-receivers in wideband CDMA networks

The synchronization performance of the receivers may severely impact the capacity or spectrum efficiency of wideband code division multiple access (CDMA) networks. Evaluations of the uplink capacity for improved spatio-temporal array receivers (STAR) and the two-dimensional RAKE (2-D-RAKE) with both perfect and active synchronization indicate that synchronization with the early-late gate component of a RAKE-type receiver may constitute a bottleneck to performance improvement. Enhancement of synchronization remains a key issue. Results also suggest that STAR offers a promising alternative to the 2-D-RAKE with early-late gate, offering an average increase in spectrum efficiency up to 100% in the presence of synchronization errors at both data rates of 9.6 and 128 kb/s. This gain further increases in high Doppler and fast multipath delay drifts. Data oversampling above the chip-rate favors STAR even more. Significant simplifications are introduced in the formulation of the STAR receiver which result in a complexity comparable to the 2-D-RAKE     

非理想载波同步对多载波直扩系统的性能影响

与单载波直扩相比,多音调制直接序列扩频（Multi-tone DSSS,MT-DSSS）在相同频谱效率下具有更高的处理增益,但非正交子载波的频谱重叠导致其对载波同步更加敏感。分别在频偏及相噪两种情况下对多音调制（MT）系统载波同步误差进行随机过程建模,计算出相关检测判决统计量及平均误码率,并进行仿真验证。结论表明：在频偏条件下,频率估计误差严重干扰每个子载波的解调并对系统误码率有较大影响;不存在频率估计误差时,频偏所造成的载波间串扰（ICI）对系统性能影响较小。在相噪条件下,相同扩频码MT系统的ICI被相关检测时的低通滤波所抑制,使其与单载波直扩具有相同误码率;不同扩频码MT系统的ICI主要由扩频码互相关性引起,而与相噪基本无关。     

The effect of dislocation loops on the light emission of silicon LEDs

Remarkably strong infrared light emission was recently observed from silicon p/sup +/-n diodes. In several publications a causal relation is proposed between the larger-than-expected light intensity and the existence of lattice damage around the junction. In this letter, we present direct experimental evidence that lattice damage is in fact detrimental to the efficiency of light emission of silicon LEDs. The experiments call for a revision of the explanation for strong light emission in this type of devices.     

On synchronization techniques: performance and impact on time metrics monitoring

The paper presents an experimental comparison of device synchronization strategies to monitor quality of service (QoS) time metrics, such as the one‐way delay and the delay variation. The compared strategies are based on global positioning system (GPS), public Internet network time protocol (NTP) servers and ad hoc GPS‐based NTP servers with different treatments of the NTP traffic. The presented experimental results allow to quantitatively evaluate the level of performance achievable using each synchronization technique. Finally, considering a satellite test bed, we focus our analysis on two relevant aspects of time metrics monitoring: the impact of the synchronization errors on the metrics observation and the different values that can be measured when a metric is monitored at the application or data link level. Copyright © 2003 John Wiley & Sons, Ltd.     

Discrete-time chaotic systems synchronization performance under additive noise

In recent decades many articles have discussed the possibilities of chaos applied in communications. However, the vast majority consider in practical terms the ideal channel condition, which is clearly a restringing condition. Some papers show that when there is an additive noise, the synchronization error often disrupts communication. In this work, we present results of a comparison between synchronization error due to additive Gaussian noise when the transmitter and receiver are implemented by single or coupled maps.     

Evaluation of a quadratic performance criterion for 3-term control loops

A general procedure for evaluating a weighted mean-square-error criterion for multivariable systems is presented. By incorporating pure time delays as Padé approximations, the method may be applied to interacting computer control loops which are subjected to random load disturbances, thus leading to optimal-control-algorithm settings. A matrix solution of the integral criterion using Gaussian elimination obviates the need for standard-integral tables.     

Harmonic analysis and performance improvement of slip energyrecovery induction motor drives

Slip energy recovery induction motor drives are used in high power applications, in which by controlling the slip power a variable speed drive system is provided. However, poor power factor is a disadvantage of the system. Presence of sub-harmonics of the line frequency on the stator side is one of the special features of these drives. A phase-controlled inverter can absorb the reactive power from the supply and inject the low-order current harmonics with relatively high amplitudes to the supply. This paper simulates the harmonic content of waveforms in various points of drive at different speeds, based on the hybrid model (dqabc). Then the sinusoidal pulse-width-modulation (SPWM) control technique is used in order to improve the power factor of the drive and to weaken the injected low-order harmonics to the supply. Based on the frequency spectrum, total harmonic distortion, distortion factor and power factor, two phase control and SPWM techniques are compared and the advantage of the SPWM technique over the phase control technique is shown     

小型化高功率微波限幅器研究

电子装备现已被大量应用,在如此复杂的电磁环境下高功率微波可导致接收机灵敏度下降甚至失效。为了满足高功率微波的防护需求,介绍了一种基于PIN 二极管的小型化高功率微波限幅器,体积为34 mm×Φ9 mm。测试结果表明,在0.3~2 GHz 频带内,该限幅器实现了小信号插损小于1 dB,输入输出驻波比小于1.5;可承受脉宽100 μs,占空比0.1%,峰值功率超过1000 W,漏功率小于17 dBm。国内外尚无类似指标限幅器相关报导。该高功率微波限幅器体积小、频带宽、耐功率高,可大大提高接收机可靠性,具有广阔的应用前景。     

低泄漏限幅器的研究

采用混合集成电路设计方法 ,用 PIN二极管和检波二极管 ,在很小的腔体内制作了小型化无源微波限幅器。电参数为 :频率 f=2 .5～ 3 .0 GHz,插入损耗 IL≤ 0 .3 9d B,电压驻波比 VSWR≤ 1 .3 ,漏功率 Plim≤ 0 .5 5 m W(输入连续波 1 W)