Effects of ionospheric scintillation on differential demodulation of GPS data

Global Positioning System (GPS) receivers that must operate under fading propagation conditions can use differential phase-shift keying (DPSK) and reference bits to reliably demodulate GPS data. The demodulation performance of such receivers is analyzed for nonfading and Rayleigh fading channels. Theoretical results derived here are compared with measured error rates taken during scintillation testing of a prototype GPS/DPSK receiver.     

飞船测控跟踪功能备份方案设计与实现

针对＂神舟＂飞船测控跟踪功能没有备份的难题,首次提出利用FM（调频）跟踪接收机跟踪接收数传信号来实现跟踪功能备份。从数传信号调制特性、FM跟踪接收机组成及载波接收解调3个方面进行了理论分析,并通过FM跟踪接收机的数传信号接收解调、静态跟踪和动态跟踪试验验证了该方案的可行性和有效性。该技术在不增加辅助设备功能的基础上,通过船载测控设备中FM跟踪接收机来实现对飞船跟踪功能的备份,显著降低对飞船目标跟踪失效的风险。     

Spectral Location of Rayleigh and "m" Fading Signals in White Gaussian Noise

The classical problem is considered of locating a fading sinusoidal signal known to be present in one of several frequency " cells," each of which contains additive white Gaussian noise. The signal fading is assumed to follow the popular Rayleigh distribution, but generalizations tions to non-Rayleigh fading are included in terms of the " in" distribution due to Nakagami. The channel observation time is allowed to be either predetermined or variable (corresponding, respectively, to " fixed sample size" and " sequential" reception), and the practically important situation of intermittent signal transmissions is also examined. Results are in the form of optimal and near-optimal receiver structures, and of measures of performance.     

Performance Degradation Due to Specular Multipath Intersymbol Interference

Plots of performance degradation are used to compare the effects of fading and intersymbol interference in a two- component specular multipath digital communications channel. Similar plots are then used to compare two practical receivers designed to combat the interference. Degradation plots are shown to allow easy identification of each receiver's range of usefulness, as well as identification of variance bounds demanded of channel parameter estimates which the receivers require.     

Nonredundant error correction DQPSK for the aeronautical-satellitechannel

The performance of differentially encoded quadrature phase-shift keying (DQPSK) system employing nonredundant error correction (NEC) receivers with single- and double-error correction capability is analyzed and evaluated for the aeronautical satellite channel. The NEC is an attractive coding technique which employs differential detectors with more than one symbol delay elements and which does not introduce any redundancy as other coding schemes do. As typical for aeronautical satellite communications, a Rician fading channel with Gaussian power spectrum has been considered. Unlike the additive, uncorrelated from symbol to symbol interference such as additive white Gaussian noise (AWGN) or static cochannel interference (CCI) which has been investigated in the past, analysis of the performance in a fading channel is much more difficult. The difficulty arises from the multiplicative and correlative nature of the fading interference. Bit error rate (BER) performance evaluation results have been obtained by means of computer simulation for various channel conditions, including different values of the K-factor and the fading B_DT. These results have indicated that considerable performance gains as compared with conventional differentially detected systems are achieved for high values of K and for very fast fading. Both of these conditions are encountered in typical aeronautical communication systems. Wherever possible, heuristic explanations of the trend of the obtained BER performance evaluation results are also given     

Effect of Fading on FM Reception with Cochannel Interference

The combined effect of cochannel interference and nonselective Rayleigh fading on the reception of analog FM signals in additive Gaussian noise is analyzed. Rice's click model for the breaking region is used. Analysis in the absence of interference is performed first and the effect of modulation on the click rate is found to be nearly negligible. For the case with cochannel interference the click rate is computed in the absence of modulation. Curves are given for detected signal-to-noise ratio (SNR) versus carrier-to-noise ratio (CNR) with signal-to-interference ratio (SIR) as a parameter and SNR versus SIR with CNR as a parameter. The results agree well with recently published results of a simulation study.     

Sensitivity Analysis of Finite-Lag Receivers

This paper presents the sensitivity analysis of a class of receivers called finite-lag receivers, introduced by the authors in [1] through [3]. Since these receivers are based on the use of fixed-lag smoothing techniques, algorithms for the calculation of large-scale and small-scale sensitivities of fixed-lag smoothing are derived using a state augmentation approach. Steady-state analysis of these algorithms shows that an explicit relation can be obtained between sensitivity coefficients of fixed-lag smoothing and filtering. The specific case of sensitivity to variations in the measurement (channel) noise is considered as an example. These results are applied to study the sensitivity performance of the finite-lag receivers for analog communication. It is shown, for example, that finite-lag receivers for AM signals, besides being superior in performance [1]-[3], [11], in terms of output SNR or error variance, are also much less sensitive to the additive noise power level, compared to zero-lag receivers.     

Spread-Spectrum Signaling for Distributed Fiber Optic Systems

One of the stringent requirements on the receivers of distributed industrial fiber optic systems is fast and accurate adaptive thresholding and a wide dynamic range. This is due to the existence of variable link lengths and geometry, especially in multipleaccess situations, coupled with unipolar optical signaling. This paper analyzes the application of a simple spread-spectrum system in such fiber-optic data links. It proposes a detector model that yields a tractable expression for the probability of error. The optimum threshold and the probability of error are then related to the received optical power, bit rate, and spectrum-spreading factor. A procedure is indicated by which, based on the minimum expected received power, a spreading facor and a threshold are chosen to insure a given maximum error rate at all the receivers.     

STEREO/Waves Goniopolarimetry

The STEREO/Waves experiment is dedicated to the study of inner heliosphere radio emissions. This experiment is composed of a set of two identical receivers placed on each of the two STEREO spacecraft. The STEREO/Waves receivers have instantaneous Goniopolarimetric (GP) capabilities (also referred to as direction-finding capabilities). This means that it is possible to retrieve the direction of arrival of an incoming electromagnetic radio wave, its flux and its polarization. We review the state of the art of GP-capable radio receivers and available GP techniques. We then present the GP capabilities of the STEREO/Waves experiment. We finally show some GP results on solar Type III radio bursts, using data recorded with the Cassini/RPWS/HFR, which are very similar to the STEREO/Waves data.     

基于Simulink?的复合衰落信道仿真与分析

基于Simulink平台建立了Rayleigh-Lognormal、Ricean-Lognormal、Nakagami-Lognormal复合衰落信道的仿真模型,这些模型可用于进行单频组网的DRM系统的设计和性能分析。给出了各种复合衰落的概率密度函数、累积分布函数、平均电平交叉率、平均衰落时间的统一表达式。仿真结果验证了理论分析结果的正确性。     

The design of digital radar receivers

With the development of digital processing technology, there are emerging trends toward digitization in radar receivers design. By applying direct intermediate frequency-to-digital conversion (IF sampling) and direct digital synthesis (DDS), digital radar receivers can be designed. The digital radar receivers can obtain much higher precision and stability than analog ones; moreover, it can retain the extreme flexibility of digital techniques. This paper presents the principle, constitution and design method of digital radar receivers     

Aircraft Navigation Using Omega

This paper describes a study of those aspects of Omega navigationthat are unique to aircraft applications. The main effort of the studyis to use a digital computer to simulate the reception of Omega signals.Three principal conclusions are drawn: the poorer signal-to-noiseratio environment will not preclude reception; interfering carriers willnot preclude reception; and the required velocity-aiding accuracy isquite modest in terms of that which is readily available from inertialsystems.     

A method for automatic detection and characterization of plasma bubbles using GPS and BDS data

Detecting and characterizing Total Electron Content (TEC) depletion is important for studying the ionospheric threat due to the Equatorial Plasma Bubble (EPB) when applying the Ground-Based Augmentation System (GBAS) at low latitudes. This paper develops a robust method to automatically identify TEC depletion and derive its parameters. The rolling barrel algorithm is used to automatically identify the TEC depletion candidate and its parameters. Then, the depletion candidates are screened by several improved techniques to distinguish actual depletions from other phenomena such as Traveling Ionospheric Disturbance (TID) or abnormal data. Next, based on the depletion signals from three triangular receivers, the method derives EPB parameters such as velocity, width and gradient. The time lag and front velocity are calculated based on cross-correlation using TEC depletions and the geometrical distribution of three triangular receivers. The width and gradient of slope are then determined by using TEC depletion from a single receiver. By comparison, both the station-pair method and proposed method depend on the assumption that the EPB morphology is frozen during the short time when the plasma bubble moves between the receivers. However, our method relaxes the restriction that the baseline length should be shorter than the width of slope required by the station-pair. This relaxation is favorable for studying small-scale slope of depletions using stations of a longer baseline. In addition, the accuracy of the width and gradient is free of impact from hardware biases and small-scale disturbance, as it is based only on the relative TEC variation. The method is demonstrated by processing Global Positioning System (GPS) and BeiDou Navigation Satellite System (BDS) data on 15 August, 2018, in a solar minimum cycle.     

面向低成本GNSS接收机终端的周跳修复策略

载波相位周跳是影响低成本GNSS接收机观测质量的主要因素之一.提出了一种面向低成本GNSS接收机终端的周跳修复策略,通过两种不同观测结果的联合检测以避免时钟和星历突变导致的误修复,并利用载噪比和多项式拟合误差检测载波观测中的无效观测,旨在提升低成本接收机在多径等复杂场景下载波相位观测的可用性.该策略仅使用了单频载波相位和载噪比信息,适用于各类低成本的接收设备.分别在开阔场景和多径场景下使用小米8手机和F9P接收机进行观测试验,结果表明,所有的有效载波相位观测得到了正确修复,仅约0.7％的无效观测被误修复,验证了所提策略的有效性.     

Adaptive Maximum Likelihood Receiver for Direct-Ranging Applications

Recent interest in direct-ranging navigation methods has prompted new research into practical receiver structures which provide improved signal processing. Maximum likelihood receivers are compared with conventional phase-locked receivers by theoretical and simulation methods as phase estimators based on signal measurements only. Signal-to-noise ratio (SNR) enhancement is examined and filter recommendations made. An adaptive maximum likelihood receiver is then developed which uses both signal measurements and a priori data to improve phase estimation accuracy. Simulation results indicate a 33.3 dB processing gain yielding a ranging error standard deviation of ±15 feet for zero dB received SNR. Nonadaptive and adaptive receivers are fabricated, flight tested, and experimental results reported.     

低成本GNSS接收机芯片载波相位测量技术

当前具备载波相位测量的GNSS接收机能够实现高精度定位,但其成本高、体积大,难以广泛应用于大批量的手机、平板电脑等消费电子产品。针对ST公司的STA8090接收机芯片并改进其软件和晶振以获得载波相位信息,采用双差和三差方程测试评估载波相位测量的精度,与测绘型接收机进行对比。基于改进的STA8090接收机芯片构建双天线定姿系统原型样机,静态测试评估了相对定位和定向精度。研究结果表明,千米级静态相对定位精度优于0.01m,在1.23m基线条件下定向精度优于0.1°。因此,采用低成本GNSS接收机芯片实现高精度载波相位测量的技术方案是可行的,具备广阔的市场应用前景。     

Multipath Fading in FSK Communication Links?An Experimental al Investigation

The results of an experimental investigation of binary error rates in an FSK channel experiencing nonselective fading are presented. For all cases considered, the received frequency uncertainty is large compareded to the bit rate, requiring the use of an envelope detector rather than a matched filter. Both slow and fast fading rates are considered and include the effects of differential Doppler shift between the direct and reflected energy. A simplified mathematical analysis is presented to support the observed results. Both the theoretical examination and the data obtained demonstrate that fast fading and/or differential Doppler generally improve the link error rate performance with respect to the nonfading case.     

A One-bit Memory Receiver for Channels with Memory

A receiver is investigated with one-bit memory for communication channels with memory. The memory of the channel is characterized by the statistical correlation of the received bits due to fading. An optimal solution to the problem is considered but is found to be quite complex to implement. Therefore, a suboptimal receiver having a decision-feedback structure is examined. The performance of the receiver is shown to be better than a receiver without memory. Binary on-off keying system is considered as an example and numerical results are obtained.     

Modified Frequency Scaling Algorithm for FMCW SAR Data Processing

This paper presents a modified frequency scaling algorithm for frequency modulated continuous wave synthetic aperture radar （FMCW SAR） data processing. The relative motion between radar and target in FMCW SAR during reception and between transmission and reception will introduce serious dilation in the received signal. The dilation can cause serious distortions in the reconstructed images using conventional signal processing methods. The received signal is derived and the received signal in range-Doppler domain is given. The relation between the phase resulting from antenna motion and the azimuth frequency is analyzed. The modified frequency scaling algorithm is proposed to process the received signal with serious dilation. The algorithm can effectively eliminate the impact of the dilation. The algorithm performances are shown by the simulation results.     

调频连续波SAR改进的频率尺度变换算法(英文)

本文提出了一种调频连续波SAR改进的频率尺度变换算法。调频连续波SAR在运动过程中持续不断地发射和接收信号,这种运动导致了回波信号的伸缩,对波前重建产生了严重的影响。推导了回波信号模型,给出了信号的距离-多普勒域表达式,分析了由于天线不断运动而导致的相位变化与方位向频率之间的关系。改进的频率尺度变换算法补偿了这种相位变化,实现了目标的精确成像,仿真结果表明了分析的正确性和算法的有效性。