Analysis of GPS and Loran-C performance for land vehicle navigationin the Canadian Rockies

Loran-C and GPS were assessed for vehicular navigation along selected roads of British Columbia during the winter of 1991. The general topography of this mountainous area is described, together with the specific topographic features and tree coverage characteristics of the 2000 km of roads tested on the mainland and on Vancouver Island. The configuration and characteristics of the Loran C Canadian West Coast chain along the roads used are described. The portable vehicle-mounted system used to collect and analyze the Loran-C and GPS signals along road profiles is described. The performance of Loran-C is analyzed in terms of signal to noise ratios (SNR), field strength, and time-difference distortions, as measured by differential GPS. These distortions, which can reach several hundred meters over distances of less than 20 km, are analyzed in terms of topographic features. The possibility of using these time-independent distortions to calibrate Loran-C for use along the above roads is discussed. Masking of GPS signals due to topographic features and tree coverage along the roads is analyzed. A comparative analysis of both Loran-C and GPS is presented in terms of signal availability and accuracy     

Hard Limiting and Sequential Detection Applied to Loran-C

The combination of an antenna, a 100 kHz bandpass filter, a hard limiter, and a sequential detector can supply highly accurate Loran-C data to a digital processor, even under low signal-to-noise-ratio conditions. For such a simple, low-cost receiver, calculations are given for the accuracy of the envelope and phase tracking of the Loran-C signal as a function of the signal-to-noise (Gaussian and atmospheric) ratio, averaging time, and radian speed of the observer with respect to the transmitter. Mentioned are the quasi-noise censoring effects of the hard limiter. Besides the Loran-C application, the hard limiter-sequential detector system can in general be applied for low-cost, synchronous signal detection under poor signal-to-noise ratio.     

Carrier-wave interference to Loran-C: a statistical evaluation

Loran-C is a pulsed, hyperbolic radio aid for long-range marine, air, and land navigation. The worldwide expansion of Loran-C, especially in Europe, has focused attention on carrier-wave interference to the system. The effects of a multiplicity of carrier-wave interferers (CWIs) on receiver timing measurement accuracy are considered. Both the phase tracking and the cycle-selection performance of receivers are quantified in terms of the probabilities that they will operate correctly within the arbitrarily set error limits. Characteristic functions (CFs) are used to compute these probabilities. Analyses and results are presented for typical situations. The relative sensitivity of the phase tracking and cycle-selection functions to interfering signals are discussed     

The Effect of Aircraft Lateral Dynamics on Aircraft Positioning Accuracy When Using Loran-C

The dynamics of an aircraft following a fixed course line using Loran-C for position fixing are shown to interact with Loran-C receiver dynamics to result in cross-track aircraft positioning errors that are smaller than cross-track Loran receiver errors. In a particular case considered, this error reduction is on the order of 50 percent.     

Microminiature Loran-C Receiver/Indicator

A Loran-C Receiver is used as an example to show how an analog system could be converted to a digital one to take advantage of the expanding integrated circuit technology. The digital equivalents of the analog servo elements are described. Criteria for the design of a phase-tracking servomechanism is developed in detail. The Loran performance requirements are used to illustrate their application. The noise performance of a critically damped Type II servomechanism is derived in detail. Since the system will be employed in aircraft, tracking velocity becomes an important consideration. An analysis is made showing that an adaptive control is desirable.     

Loran-C cycle identification in hard-limiting receivers

A new technique is presented for use in hard-limiting receivers. It is based on the widely used analogue “half-cycle peak ratio” (HCPR) technique, from which it differs by being entirely digital; no additional analogue signal processing or other hardware is required. Drawing on recent advances, the new method makes decisions based on a large number of sample points in each Loran-C pulse, thereby increasing the resilience of the identification process in the presence of noise. Performance of the algorithm in the face of continuous-wave interference is equal to or better than that of other cycle-identification techniques     

Eigen-decomposition techniques for Loran-C skywave estimation

Eigen-decomposition spectral analysis techniques are used to estimate the delays of Loran-C skywaves. Their performance is evaluated and compared with that of Fourier-based techniques. Results using off-air data are presented. This work establishes the basis on which to design a Loran-C receiver capable of adjusting its sampling point adaptively to the optimal value in a constantly changing skywave environment. Such receivers promise to improve significantly the accuracy and reliability of positioning under adverse operational conditions.     

GPS速度法确定飞机空速系统位置误差

飞机空速系统位置误差的测定,飞行试验中有多种常规方法,但期精度只能满足常规型号空速系统的验证要求。针对这一问题提出了ＧＰＳ速度法,叙述了该方法的原理、实施过程和数据处理方法,讨论了方法的系统精度并给出了误差估算结果。通过对某型飞机的验证试飞,表明该方法简便易行,可满足气动补偿型空速系统的试飞验证要求。     

High-efficiency Loran-C interference identification by synchronous sampling

A new technique is proposed for estimating the frequencies within carrier-wave interference (CWI) affecting Loran-C receivers. Its novelty lies in that interference samples are taken synchronously with the Loran-C pulses and ensemble-averaged in the time domain prior to conventional spectrum analysis. Each interferer is thus automatically weighted according to its effect on the phase tracking operation of the receiver. The new method substantially increases the efficiency with which the most insidious interferers may be pinpointed. It requires little additional computational power or memory in the receiver.     

A new technique for decoding Loran-C radionavigation signals

A new approach to the extraction of navigation information from Loran-C radionavigation signals is described. A reduced-rate time-reversed sequence is derived from the RF signal and processed by a finite-impulse response (FIR) filter. It is shown that proper design of the FIR filter and proper control of the sampling point guarantee the rejection of skywave contamination, and achieve excellent rejection of continuous-wave interference (CWI). The process is computationally efficient     

利用GPS进行姿态估计的一种算法

首先建立了全球定位系统（ＧＰＳ）姿态确定的观测方程;然后给出了利用ＧＰＳ进行飞行器姿态估计的模型,并对该模型进行了线性处理;最后利用攻推广卡尔曼滤波技术,针对某飞行器进行了仿真计算。计算结果表明,对于不同的测量噪声和系统噪声,滤波器都有较好的估计,姿态估计的精度明显高于单纯ＧＰＳ姿态确定的精度,可以满足大多数飞行器对姿态确定的要求,证实了模型和算法可用性。     

北斗／罗兰-C组合定位技术

“北斗一号”是我国的卫星导航系统,其有源定位模式使其很难得到广泛应用。为此,提出了一种北斗／罗兰-C组合定位方案以实现无源定位。该方案利用“北斗一号”两颗卫星和地面罗兰-C台站获得的距离差信息实现双曲线相交定位。仿真结果表明,该方案的精度可以满足一般定位要求,具有较强的实用性。     

一种容腔效应标定技术及其在高频响动态探针中的应用

介绍一种容腔效应标定方法,以理论模型推导与实验验证相结合的方式,完成了对高频响动态探针的动态标定,并通过ARMAX(自动回归滑动平均)模型辨识得到了容腔的传递函数.结果表明该方法简单可行,能够很好地通过探针的动态响应信号来确定探针容腔的传递函数,从而确定测量信号和真实信号之间的关系,对今后考虑容腔效应的动态标定提供了参考.      

High Dynamic GPS Receiver Using Maximum Likelihood Estimationand Frequency Tracking

A new high dynamic global positioning system (GPS) receiver ispresented and its performance characterized by analysis,simulation, and demonstration. The demonstration receiver is abreadboard model capable of tracking a single simulated satellitesignal in pseudorange and range rate. Pseudorange and range rateestimates are made once every 20 ms, using a maximum likelihoodestimator, and are tracked by means of a third-order fadingmemory filter in a feedback configuration. The receiver trackspseudorange with rms errors of under 1 m when subjected tosimulated 50 g, 40 g/s circular trajectories. The tracking thresholdis approximately 28 dB·Hz, which provides 12 dB margin relativethe the minimum specified signal strength, assuming 3.5 dB systemnoise figure and 0 dB antenna gain.     

对GPS／INS制导巡航导弹GPS干扰方法的探讨

目前GPS/INS制导已成为精确制导武器的核心。本文根据GPS信号特点及GPS/INS制导机理,通过对压制干扰和欺骗干扰技术及其对GPS接收机影响的分析,着重探讨对GPS/INS制导巡航导弹GPS干扰的方法。若要提高对GPS/INS制导巡航导弹实施远距离干扰的效果,而又使干扰机功率不是很大,则需建立多层次、分布式、立体式、小功率GPS干扰体系。     

Civil Access to NAVSTAR GPS

US government policy is established and procedures are being formulated to direct the implementation of techniques providing limited civil access to full GPS accuracy. The results of these efforts balance the conflicting needs of civil GPS navigation and positioning against national security requirements. Granting this access will require sufficient and demonstrable user need, must clearly provide for both national and security interests, and may lead to the imposition of a user service charge. This access will only apply to Precise Positioning Service configured, code-tracking GPS receivers.     

基于小波变换的GPS载波相位周跳检测与修复

载波相位周跳检测与修复是实现GPS高精度定位的难点之一。小波变换具有空间局部性好的特点,本文利用小波变换把载波相位观测量分解为高频和低频分量,提出了利用小波系数局部极值点检测相位周跳的方法。基于载波相位和多普勒频率共同约束的埃尔米特多项式,外推周跳时刻载波相位,与观测值比较确定周跳的大小,从而修复周跳。利用飞机实际观测数据和仿真的高动态数据进行了计算,给出了计算结果,表明该方法可以对高动态情况下载波相位周跳进行准确探测和修复。     

An Automatic Timing Receiver System Based on the Loran-C Navigational Network

This paper describes some new concepts in dealing with the circuitry for Loran-C automatic timing systems. The conventional analog techniques associated with phase-adjusting networks have been replaced by an incremental digital phase-shifting device. The Loran-C period generator includes facilities for delay compensation by means of an epoch monitor producing a 1-Hz output coincident with the master station TOC (time of coincidence). The required initial time information has to be accurate within ± 20 ms. The automatic format identification and decoding equipment together form a system which takes into account the information of every Loran-C pulse. Owing to the use of digital signal treatment, the synchronization accuracy is limited only by the resolution of the incremental phase shift. The automatic cycle selection device is based on sampling techniques where the derivative of the envelope is calculated. The time of coincidence has to be precalculated and fed into the thumbwheel memory of the epoch monitor, which is automatically initiated when the synchronizing operations are concluded. For VLBI purposes and transcontinental use, the accuracy of this system will be better than 1 ?s when post corrections, supplied by the U.S. Naval Observatory, are taken into account.     

基于apFFT的罗兰-C窄带干扰频域抑制方法

针对现有罗兰-C接收机普遍采用固定陷波电路抑制窄带干扰的情况,提出了基于全相位谱分析(apFFT)的频域精确自适应陷波罗兰-C窄带干扰抑制方法,设计了基于双相移组合全相位法的FIR频域陷波器。在对窄带干扰进行精确谱分析的基础上,设计相应频点的陷波器对多个窄带干扰进行抑制。基于MATLAB的仿真结果表明:该方法能够根据罗兰-C窄带干扰频率的变化,实现频点任意控制的频域自适应陷波,有效恢复出罗兰-C信号,为增强型罗兰-C接收机的设计提供了一种简单有效的窄带干扰抑制方法。     

Global Gravity Field Recovery Using Solely GPS Tracking and Accelerometer Data from Champ

A new long-wavelength global gravity field model, called EIGEN-1, has been derived in a joint German-French effort from orbit perturbations of the CHAMP satellite, exploiting CHAMP-GPS satellite-to-satellite tracking and on-board accelerometer data over a three months time span. For the first time it becomes possible to recover the gravity field from one satellite only. Thanks to CHAMP'S tailored orbit characteristics and dedicated instrumentation, providing continuous tracking and on-orbit measurements of non-gravitational satellite accelerations, the three months CHAMP-only solution provides the geoid and gravity with an accuracy of 20 cm and 1 mgal, respectively, at a half wavelength resolution of 550 km, which is already an improvement by a factor of two compared to any pre-CHAMP satellite-only gravity field model. This revised version was published online in August 2006 with corrections to the Cover Date.