An Unambiguous Tracking Method Based on Pseudo Correlation Function for AltBOC(15,10) Signal

The Galileo E5 or COMPASS B2 signal is the most precision civil and most challenging navigation signal which will be available in the near future for regular navigation. The excellent performance of this signal was reached by Alternative Binary Offset Carrier (AltBOC) modulation, which is specially designed for high precision range measurement and which is featured by extremely wide bandwidth. However, this modulation presents some drawbacks. The most severe one is the ambiguity problem in AltBOC signal acquisition and tracking, which introduces a large bias in the pseudo-range measurement. In order to solve this problem, an unambiguous tracking method based on a pseudo correlation function for AltBOC(15,10) modulation signal is proposed in this paper. It employs two local signals and a novel combination function, which completely removes side peaks from the correlation function while keeping the sharp main peak. Impacts of multipath on the proposed method are also investigated. Simulation results demonstrate that the proposed method is totally unambiguous while exhibiting an average multipath performance with respect to the existing unambiguous tracking methods.     

一种新颖的GNSSBOC信号无模糊相关技术研究

现代GNSS卫星导航系统建设中,采用了BOC、MBOC和AltBOC等新体制信号。新体制信号虽然有优于BPSK信号的性能,但其相关函数的多副峰特性导致其较传统BPSK信号难于捕获和跟踪,特别是在多径环境下,难度进一步加大。本文首先对BOC信号的数学特性及模糊问题成因进行了分析,进而提出了一种新的BOC相关函数无模糊相关技术。最后,通过Matlab仿真验证了算法的有效性,为BOC信号无模糊跟踪的工程实现奠定理论基础。     

Code phase discrimination function shaping method for Compass B1C QMBOC (6,1,4/33) signal

The discrimination function shaping method has been proposed to improve the anti‐multipath performance for a global navigation satellite system receiver. However, the existing methods fail to fully exploit the potential anti‐multipath performance of multiplexed binary offset carrier (MBOC)–modulated signals. In this paper, a code phase discrimination function shaping method is proposed for a Compass B1C quadrature MBOC‐modulated signal. The in‐phase binary offset carrier (BOC) (1,1) signal and quadrature‐phase BOC (6,1) signal replicas are designed according to the least squares estimation. Then a shifted cross‐correlation function (CCF) between the in‐phase BOC (1,1) signal and its pseudorandom noise code is multiplied with the obtained CCFs to ensure an unambiguous tracking. Finally, a discrimination function with a small pull‐in range can be obtained by a weighed combination of the in‐phase and quadrature‐phase CCFs. A computer simulation is conducted to assess the performances under multipath and thermal noise conditions.     

Multipath Mitigation Technique Based on Partial Autocorrelation Function

GPS positioning accuracy in indoor and urban canyons environments is greatly affected by multipaths due to distortions in its autocorrelation function. In this paper, the first sidelobe of Pseudorandom Noise (PN) code autocorrelation is studied and a new multipath mitigation technique based on PN code autocorrelation function is presented. This new technique relies on the detection of the partial autocorrelation function that is affected by multipath signals. The increase in fractional delay of the line-of-sight (LOS) signal is calculated. Simulation results indicate that the proposed technique has superior performance compared with the 0.1-chip-spacing narrow correlator on mitigating multipath signals, especially the short-delay multipath signals. Zhang Zhen obtained his Bachelor’s Degree from Beijing Information and Technology Institute in 1999, Master’s Degree from Tsinghua University, Beijing China, in 2002. He now is a Ph.D. student in Nanyang Technological University. Currently he also works as a Research Associate in the Positioning and Wireless Technology Center (PWTC), NTU. His research interest includes multipath mitigation for GPS, software GPS receiver design, indoor GPS as well as Ultra Wide Band (UWB) based ranging systems. C. L. Law is an Associate Professor in School of EEE, NTU and the Director of PWTC. Dr. Law’s current research area is in Wireless Networks. His research topics are in microwave integrated circuits, indoor wireless channel modeling, analysis of indoor wireless LAN performances and in techniques for overcoming the time-dispersion distortions in high speed wireless LAN. E. Gunawan is an Associate Professor in School of EEE, NTU and his research interest includes Error Correction Codings, Modeling of Cellular Communications Systems, Power Control for CDMA Cellular Systems, MAC Protocols, Multicarrier Modulations, Multiuser Detections, Space-time Coding, Radio-location Systems, UWB and its applications for Human Body Vital Signs Detection, and Powerline Communications.     

A modified PN code tracking loop for direct-sequencespread-spectrum communication over arbitrarily correlated multipathfading channels

A modified fully digital pseudonoise code tracking loop is proposed for direct-sequence spread-spectrum communication. By taking advantage of the inherent diversity, a modified code tracking loop is embedded into a RAKE receiver in order to avoid problems caused by unstable locked points of error signals. Such unsteadiness of locked points often occurs with a conventional code tracking loop because the error signals may be randomly biased by multipath fading. Thus, a robust pull-in capability can be provided over a time-variant fading channel where multiple propagation paths are arbitrarily correlated. Furthermore, an effective multipath interference regeneration and cancellation technique is also proposed to improve the error characteristics of the proposed technique. Analytical expressions of the error characteristics and error signals are derived and then confirmed by means of extensive computer simulation results. In addition, several simulation results for the timing jitter and the mean time to lose lock are also presented. The very attractive behavior obtained using the proposed technique is verified     

Unambiguous and precise correlation receiver for binary offset carrier modulated signal

The binary offset carrier (BOC) modulated signal can improve the positioning accuracy and increase the multipath resistance in global navigation satellite system (GNSS), and it may cause potential ambiguity in the process of signal acquisition and code tracking. In this paper, a simple but efficient unambiguous receiver is firstly proposed for multiple side‐peaks mitigation by implementing correlation of the received BOC signal with local sine wave instead of square wave used at the transmitter. Moreover, the potential degradation of sharpness of the nonlinear correlation induced by the sine wave is well compensated by optimizing the early‐to‐late spacing. The other reason leading to ambiguity is the multipath propagation, so we further propose a maximum likelihood (ML) estimator with Newton iteration method, where the received GNSS signal is modeled via the line‐of‐sight (LOS) component and the first‐arrived non‐line‐of‐sight (NLOS) component. Finally, the analytical expression of multipath propagation Cramer‐Rao bound is derived for the designed ML estimator. Simulation results indicate that compared with the conventional BOC modulation, the proposed sine wave receiver can achieve unambiguous and more precise code tracking performance and thus turns out to be more robust to multipath propagation.     

GNSS CODE AND CARRIER TRACKING IN THE PRESENCE OF MULTIPATH

It is well known that multipath represents a major error source in differential GNSS positioning. Errors produced are unique to each antenna position and so are uncorrelated between the reference station and the mobile receiver. Reduction techniques, such as narrow correlator spacing¹ and the multipath estimating delay lock loop (MEDLL)² have improved the situation. However, reflected signals emanating close to the antenna are not reduced by either technique. Carrier multipath is a particular problem because short delay multipath signals cause maximum carrier errors. This study describes the analysis that has been carried out into code and carrier tracking in the presence of multipath. Code tracking in this situation produces a non-zero mean error,³ and the source of this bias has been investigated. Code and carrier multipath errors of the global orbiting navigation satellite system (GLONASS) have been compared with those of the global positioning system (GPS). The effects of pre-correlation filtering on code and carrier multipath errors have been determined using data from a measured correlation function. The multipath fading bandwidth is also discussed, and fast and slow fading effects are presented. A comparison has been made of the performance of typical coherent and non-coherent code discriminators in the presence of multipath. The performance of the GPS and GLONASS P code signals have been determined with respect to code and carrier multipath errors. © 1997 by John Wiley & Sons, Ltd.     

GPS系统中的多径效应分析

本文研究了ＧＰＳ系统中多径效应的伪唬测量误差，先分析镜面多径信号的时间延迟和由此引起的频带扩展，然后研究在用相干和非相干延时锁定环跟踪ＰＮ码信号时多径信号对Ｓ曲线的影响和由此带来的伪距测量误差（多径误差）以及减小多径误差的方法。     

基于盲判决反馈均衡的GPS信号多径干扰抑制方法

给出了存在多径效应时的GPS接收信号模型,分析了多径干扰对GPS接收机跟踪环路的影响,将均衡技术应用于跟踪环路,提出了一种GPS信号多径干扰抑制方法.该方法在GPS信号跟踪环路中引入了判决反馈分数间隔均衡器,同时,根据GPS信号为BPSK调制且发送的伪码序列被导航电文调制后存在正负反转不确定性的特点,均衡器系数更新时选...     

Tailored spreading symbols in “Strobe Correlators” using “W2-pulses”

A “Strobe Correlator” is a correlation-based multipath mitigation technique that utilizes tailored reference waveform to shape the discriminator function for tracking Global Navigation Satellite System (e.g. Global Positioning System) signals. Multipath performance of these techniques for Binary Phase Shift Keying (BPSK) signals has been discussed for decades but for some, their noise performance may not be easily evaluated analytically. In this paper, a theoretical framework is provided for noise evaluation of “Strobe Correlators” using complex strobes for both BPSK and sine-phased Binary Offset Carrier (e.g. BOC(1,1)) signals. Mathematical expressions of the tailored spreading symbols as key factors are derived and used for theoretical code tracking variance analysis of various correlation techniques including the “Gating Function” using a complex strobe-pulse liked waveform (i.e. “W2-pulses”). Empirical results for the sine-phased BOC(1,1) signal are given as verification. Analytical results reveal that the techniques using a W2-pulse suffer from higher code tracking variance than others, due to increased sensitivity to noise. The sensitivity to pre-correlation bandwidth is found to relate to the relative placement of the strobe pulses.     

Correlation functions of BOC and AltBOC signals as the inverse Fourier transforms of energy spectra

The navigation signals with sine binary offset carrier (sinBOC), cosine BOC (cosBOC), and alternative BOC (AltBOC) modulations are discussed. A technique for calculating the correlation functions (CFs) of the single components of modulating functions (MFs) inherent to the given signals, which is based on the inverse Fourier transform (IFT) of energy spectra, is proposed. This technique makes it possible to derive analytical expressions for the CFs characterizing the single components of the MFs of sinBOC and cosBOC signals and complete AltBOC waveforms with a constant envelope at the multiplicity coefficients N_m = 2?4. The graphs of CFs are constructed. Several illustrating examples, in which most attention is paid to sinBOC, cosBOC, and AltBOC signals employed in the Galileo satellite radio-navigation system and the global positioning system, are presented.     

现代OS导航信号中HRC相关间隔的优化设计

目前接收机基于环路的多径抑制主要采用窄相关和HRC技术,而在实际应用中HRC技术对不同调制方式的现代导航信号采取的相关间隔也不同。针对上述问题,通过对几种现代导航信号的鉴相范围和多径抑制性能进行分析,给出在现代导航信号中HRC鉴别器算法相关间隔的优化设计方法。仿真可见:不同现代导航信号下HRC相关间隔的优化选取也不同;带宽较宽时,鉴相范围随相关间隔增大而增大,多径抑制性能随相关间隔减小而提高;带宽较窄和相关间隔较小时,在一定鉴相范围内减小相关间隔并不会再提高现代导航信号的多径抑制性能。提出的相关间隔的优化方法具有创新性,研究成果具有重要理论价值并已应用到GNSS接收机中。     

Blind RAKE receiver with joint diversity combining and codetracking for DS/SS communication

A RAKE receiver achieving joint blind multipath diversity combining and code tracking is proposed. An improved known modulus adaptive algorithm is exploited to perform multipath diversity combining and to support the modified code tracking in the blind mode. Computer simulation results have indicated very attractive behaviour of the proposed technique     

Pseudonoise code tracking loop for a CDMA system with imperfect power control

In this paper, performance of a pseudonoise (PN) code tracking loop is analysed and simulated for a direct‐sequence/code‐division‐multiple‐access (DS/CDMA) system with imperfect power control in a multipath fading channel. A non‐coherent first‐order delay‐locked loop (DLL) is considered as a PN code tracking loop. Power control error is modelled as a log‐normally distributed random variable. The multipath fading channel is modelled as a two‐ray Rayleigh fading model that is typically applied to land mobile communication environments. The tracking performance of DLL is evaluated in terms of tracking jitter and mean‐time‐to‐lose‐lock (MTLL). From the simulation results, it is shown that for smaller discriminator offset, tracking jitter performance is improved while MTLL performance is degraded. It is shown that large power control error and heavy shadowing substantially degrade the PN tracking performance. Therefore, an accurate power control scheme is very essential to compensate for fading and shadowing for a DS/CDMA system. The extension of analysis to higher‐order loop models is very straightforward. The analysis in this paper can be applied to design the PN code tracking loop for a DS/CDMA system. Copyright © 2001 John Wiley & Sons, Ltd.     

一种新的GPS多径抑制方法

随着GPS(全球定位系统)技术的广泛应用,人们对GPS的定位精度提出了越来越高的要求,有的已经要求达到cm甚至mm级。差分GPS系统虽然可以消除大部分定位误差,提高定位精度,但是还是无法消除多径信号引起的定位误差。介绍了GPS中多径信号的影响,分析了TK算法和多径监视(MPI)算法抑制多径的优缺点。通过将这2种算法级联,提出了一种新的混合方法(TK-MPI算法),并且取得了更好的定位精度,特别是在低信噪比的情况下具有很好的效果。     

A low‐complexity adaptive receiver for DS‐CDMA systems in unknown code delay environment

In direct‐sequence code division multiple access (DS/CDMA) multiuser communication systems in multipath channels, both intersymbol interference (ISI) and multiple‐access interference (MAI) must be considered. The multipath channel characterizes the propagation effects including the timing offset and delays, etc. Traditionally, we use the delay‐locked loop (DLL) code tracking loop to recover the timing delay. But DLL cannot work well in multipath environment. In this paper, we propose a low‐complexity adaptive receiver to suppress ISI/MAI and solve the timing offset problems without using conventional DLL code tracking loop. The proposed receiver employs an adaptive filter whose weights are adapted using a block least‐mean square error algorithm with fractional sampling. Simulations confirm the good performance, including learning curves and theoretical analysis of minimum mean‐square error, of the proposed receiver. Copyright © 2010 John Wiley & Sons, Ltd.     

Galileo接收机的多径误差分析与研究

多径是影响卫星定位系统的主要因素,因此如何消除多径成为提高定位精度的重要任务。以Galileo接收机为基础来研究多径的抑制。主要介绍了Galileo信号和多径信号的基本结构,通过对多径消除方法——窄相关技术的仿真,可以看出,窄相关技术对跟踪误差有很好的抑制能力,能提高测量精度。     

异步DS-CDMA系统盲空时信道估计及多用户检测

该文提出了适用于频率选择性瑞利衰落信道中的异步DS-CDMA系统盲空时信道估计及多用户检测算法。通过研究多径信号码空间和数据矢量空间,采用噪声子空间技术进行异步DS-CDMA系统盲空时信道参数估计,同时利用了多径传播和接收机同步失调的特性,以利于把盲线性滤波优化技术应用于稳健的干扰抑制。使用一种修改的ULV更新算法进行噪声子空间跟踪,该算法不需要相关矩阵的秩估计,直接估计噪声子空间,不进行信号子空间跟踪。并且研究了线性约束最小方差(LCMV)盲空时多用户检测及其基于Householder变换约束最小均方算法(HCLMS)的自适应实现。仿真结果验证了该文算法的有效性。     

同阶二元偏移载波调制信号跟踪技术

针对同阶二元偏移载波调制卫星导航信号,提出一种高效新算法解决信号跟踪中的模糊性。分析了同阶二元偏移载波调制原理、信号跟踪模糊性及解决方法,利用本地扩频码与接收信号的相关函数特点,构建了码跟踪环路鉴相曲线,选择了合适的相关间距作为符号判决,联合构成鉴相器,推导了算法设计的正确性,给出了实现架构。仿真结果表明,码相位捕获误差±0.9个码片内均可正确跟踪。该方法可进一步应用于全球卫星导航系统新体制信号的接收处理。     

改进K-means算法对AltBOC信号组合码序列的盲估计

针对恒包络交替二进制偏移载波(Alternate Binary Offset Carrier, AltBOC)调制信号组合码序列难以估计的问题，提出了利用改进K-means算法进行信号组合码盲估计方法。该方法首先通过引入互调分量以及重建副载波的方式构建AltBOC信号模型，然后在接收端将AltBOC信号分段成单倍组合码周期窗长的不重叠观测数据矩阵，并利用相似性原理从观测数据中选择最优的样本作为K-means聚类中的初始均值向量，最后通过K-means算法迭代优化数据样本与其聚类均值向量的平方误差，完成对AltBOC信号组合码序列的盲估计。计算机仿真结果表明，利用该算法在信噪比-15dB下能够较为精确地估计AltBOC信号组合码序列。