Multiple Constellations Research Articles

Low-complexity fractional phase estimation for totally blind channel estimation

To remove the scalar ambiguity in conventional blind channel estimation algorithms, totally blind channel estimation (TBCE) is proposed by using multiple constellations. To estimate the unknown scalar, its phase is decomposed into a fractional phase and an integer phase. However, the maximum-likelihood (ML) algorithm for the fractional phase does not have closed-form solutions and suffers from high computational complexity. By exploring the structures of widely used constellations, this paper proposes a low-complexity fractional phase estimation algorithm which requires no exhaustive search. Analytical expressions of the asymptotic mean squared error (MSE) are also derived. The theoretical analysis and simulation results indicate that the proposed fractional phase estimation algorithm exhibits almost the same performance as the ML algorithm but with significantly reduced computational burden.

Performance Analysis of GPS/BDS Precise Point Positioning

Precise Point Positioning (PPP) with GPS measurements has achieved a level of success. In order to benefit from the multiple available constellations, research has been undertaken to combineGPS and BDS measurements in PPP processing.Mathematical models of GPS/BDS combined precise point positioning are introduced in this paper. GPS/BDS combined PPP models are developed based on the GPS-only PPP. The data pre-processing steps include applying satellite orbit and clock corrections, satellite antenna phase offset correction, receiver antenna phase offset correction, differential code bias corrections, troposphere delay corrections and the the Ionosphere-free observation combination is used. The results show that the positioning precision and convergence speed of GPS/BDS combined PPP are improved compared with GPS-only PPP.

Signal Interference between GPS and Wide Area Augmentation System

With the development of Global Navigation Satellite System (GNSS), multiple constellations broadcasting more signals in the same frequency bands will cause interference effects on the systems. At a min- imum, all GNSS signals and services must be compatible. In this paper, a complete methodology for the signal interference assessment is presented. Real simulations accounting for the interference effects were carried out on the L1 band where GPS and Wide Area Augmentation System (WAAS) are sharing the same band. And the re- sults show that the WASS can provide a sound basis for compatibility with GPS.

GNSS Multipath and Jamming Mitigation Using High-Mask-Angle Antennas and Multiple Constellations

Multipath and jamming interference affects the accuracy, availability, and continuity of global navigation satellite systems. The U.S. Global Positioning System and the Russian Global'naya Navigatsionnaya Sputnikovaya Sistema (GLONASS) are being joined by the European Galileo and the Chinese BeiDou. An increasing number of satellites in multiple constellations enable users to use high-mask-angle antennas (HMAAs) to mitigate interference signals coming from a low-elevation angle. This paper studies the optimal antenna mask angle that maximizes the suppression of interference but still maintains the performance of a single constellation with a low-mask-angle antenna. This paper first proves a novel lower bound on the expectation of dilution of precision (DOP) and derives closed-form formulas that relate the lower bound to the antenna mask angle and the number of satellites. Then, through extensive simulations, a variety of optimal mask angles are obtained with respect to different constellation settings, different DOP metrics, and different assumptions of range accuracy. The numerical results highly agree with our theory. Both of them show that two constellations can match the performance of one constellation with a 5 $^{\circ}$ –14 $^{\circ} $ higher mask, and three constellations can match the performance of one constellation with an 11 $^{\circ}$ –23 $^{\circ} $ higher mask, depending on the DOP metric and the range error model used. The numerical results also show that using HMAAs is more beneficial to users interested in positioning accuracy than to users interested in time transfer accuracy.

A Genetic Algorithm for Generating Radar Transmit Codes to Minimize the Target Profile Estimation Error

AbstractThis article presents the design and development of a genetic algorithm (GA) to generate long-range transmit codes with low autocorrelation side lobes for radar to minimize target profile estimation error. The GA described in this work has a parallel processing design and has been used to generate codes with multiple constellations for various code lengths with low estimated error of a radar target profile.

New methods for dual constellation single receiver positioning and integrity monitoring

Navigation system integrity monitoring is crucial for mission (e.g. safety) critical applications. Receiver autonomous integrity monitoring (RAIM) based on consistency checking of redundant measurements is widely used for many applications. However, there are many challenges to the use of RAIM associated with multiple constellations and applications with very stringent requirements. This paper discusses two positioning techniques and corresponding integrity monitoring methods. The first is the use of single frequency pseudorange-based dual constellations. It employs a new cross constellation single difference scheme to benefit from the similarities while addressing the differences between the constellations. The second technique uses dual frequency carrier phase measurements from GLONASS and the global positioning system for precise point positioning. The results show significant improvements both in positioning accuracy and integrity monitoring as a result of the use of two constellations. The dual constellation positioning and integrity monitoring algorithms have the potential to be extended to multiple constellations.

History and critical marketing studies

PurposeThe purpose of this paper is to argue that the function of history in critical marketing studies centres on the issue of contextualisation. It aims to put forward the idea that historically informed critical marketing studies highlight that key institutions, actors and scholarly writings have all helped to constitute, perform and destabilise marketing theory, thought and practice in ways that reflect multiple constellations of interests.Design/methodology/approachBy way of an engagement with various strands of the literature, it is suggested that the history of marketing thought and marketing history are riven with power relations. They include economically derived power relations and culturally significant changes in the social environment. However, while important, they are only part of a more pluralistic tapestry of factors that come from sometimes completely unrelated areas that helped constitute the conditions which fostered a given area of inquiry, debate and so on, in marketing and consumer research.FindingsWeaved into accounts such as those articulated within critical marketing studies are attempts to rethink aspects of theory, concept formation, thought, practice and institutions that have assumed a taken‐for‐granted status.Originality/valueThis account is based on a detailed reading of interdisciplinary debates read into the history of marketing thought and marketing history.

Reliability of partial ambiguity fixing with multiple GNSS constellations

Reliable ambiguity resolution (AR) is essential to real-time kinematic (RTK) positioning and its applications, since incorrect ambiguity fixing can lead to largely biased positioning solutions. A partial ambiguity fixing technique is developed to improve the reliability of AR, involving partial ambiguity decorrelation (PAD) and partial ambiguity resolution (PAR). Decorrelation transformation could substantially amplify the biases in the phase measurements. The purpose of PAD is to find the optimum trade-off between decorrelation and worst-case bias amplification. The concept of PAR refers to the case where only a subset of the ambiguities can be fixed correctly to their integers in the integer least squares (ILS) estimation system at high success rates. As a result, RTK solutions can be derived from these integer-fixed phase measurements. This is meaningful provided that the number of reliably resolved phase measurements is sufficiently large for least-square estimation of RTK solutions as well. Considering the GPS constellation alone, partially fixed measurements are often insufficient for positioning. The AR reliability is usually characterised by the AR success rate. In this contribution, an AR validation decision matrix is firstly introduced to understand the impact of success rate. Moreover the AR risk probability is included into a more complete evaluation of the AR reliability. We use 16 ambiguity variance–covariance matrices with different levels of success rate to analyse the relation between success rate and AR risk probability. Next, the paper examines during the PAD process, how a bias in one measurement is propagated and amplified onto many others, leading to more than one wrong integer and to affect the success probability. Furthermore, the paper proposes a partial ambiguity fixing procedure with a predefined success rate criterion and ratio test in the ambiguity validation process. In this paper, the Galileo constellation data is tested with simulated observations. Numerical results from our experiment clearly demonstrate that only when the computed success rate is very high, the AR validation can provide decisions about the correctness of AR which are close to real world, with both low AR risk and false alarm probabilities. The results also indicate that the PAR procedure can automatically chose adequate number of ambiguities to fix at given high-success rate from the multiple constellations instead of fixing all the ambiguities. This is a benefit that multiple GNSS constellations can offer.

Adaptive Decision-Feedback Detection With Constellation Constraints for MIMO Systems

A novel low-complexity decision-feedback detection algorithm with constellation constraints (DFCC) is proposed for multi-input-multi-output (MIMO) systems. An enhanced interference cancellation is achieved by introducing multiple constellation points as decision candidates. A complexity reduction strategy is also developed to avoid redundant processing with reliable decisions. For time-varying channels, the proposed receiver updates the filter weights using a recursive least-squares (RLS)-based algorithm. This efficient detector is also incorporated in a multiple-branch (MB) structure to achieve a higher detection diversity order. A soft-output DFCC detector is also proposed as a component of an iterative detection and decoding receiver scheme. Simulations show that the proposed DFCC technique has complexity as low as the adaptive decision-feedback (DF) detector while it significantly outperforms ordered successive interference cancellation (OSIC) processing.

Genetic Algorithm for Orbital Optimization to Approach Multiple Constellation Satellites

以三颗非共轨的Walker星座卫星为研究对象, 对航天器无需变轨与其接近的可能性进行研究. 将Lambert方法得到的航天器轨道作为初始轨道, 利用遗传算法对初始轨道进行优化. 对初始轨道在参考时刻位置和速度的改变量进行编码,形成对应的种群. 以航天器与星座卫星之间的最近距离为适应度函数, 通过种群的繁殖得到优化结果. 结合仿真算例, 分析了最小二乘算法和遗传算法在轨道优化中的优劣以及接近过程中轨道摄动的影响. 结果表明, 遗传算法适用于所提出的轨道改进问题. 研究结果可为单航天器无需变轨对星座多星接近问题提供理论依据.

Impact of the GNSS Time Offsets on Positioning Reliability

With the development of GPS, GLONASS, Galileo, Compass, QZSS and the IRNSS, there has been growing interest in the development of system independent receivers. However, one of the problems encountered in system independent receivers is in the different time systems employed by each of the satellite navigation systems. To overcome this problem it has become a standard practice to solve for the time differences within the receiver’s navigation solution via a combination of receiver clock corrections and/or time offsets. While this technique overcomes the problem of the different time systems, it is at the cost of a satellite from each additional time system. Despite this, the numerous studies that combine multiple satellite navigation systems this way have still found that there are significant benefits in improved accuracy, integrity, continuity and availability. To enhance interoperability though satellite navigation system providers are intending to measure and transmit the time offsets to other time systems. The subsequent use of these time offsets will provide a more accurate navigation solution than without them. However, the problem with using the time offsets is that they pose an additional integrity risk because they are also potential sources of faults. However, with the use of the time offsets for multiple constellation solution, a proper Receiver Autonomous Integrity Monitoring method has not been developed. Thus, mathematical models to account for the time differences with and without the time offsets are presented in this paper. Furthermore, the model that incorporates the time offset allows the application of Receiver Autonomous Integrity Monitoring to detect the presence of any faults within the time offsets. The reliability of the linear models is then compared using GPS and GLONASS geometry in terms of the Minimal Detectable Biases, Protection Levels and the correlation coefficients. The results of this analysis indicate that a more reliable solution can be obtained with the time offsets because they are additional measurements.

Generalised DOPs with Consideration of the Influence Function of Signal-in-Space Errors

Integrated navigation using multiple Global Navigation Satellite Systems (GNSS) is beneficial to increase the number of observable satellites, alleviate the effects of systematic errors and improve the accuracy of positioning, navigation and timing (PNT). When multiple constellations and multiple frequency measurements are employed, the functional and stochastic models as well as the estimation principle for PNT may be different. Therefore, the commonly used definition of “dilution of precision (DOP)” based on the least squares (LS) estimation and unified functional and stochastic models will be not applicable anymore. In this paper, three types of generalised DOPs are defined. The first type of generalised DOP is based on the error influence function (IF) of pseudo-ranges that reflects the geometry strength of the measurements, error magnitude and the estimation risk criteria. When the least squares estimation is used, the first type of generalised DOP is identical to the one commonly used. In order to define the first type of generalised DOP, an IF of signal–in-space (SIS) errors on the parameter estimates of PNT is derived. The second type of generalised DOP is defined based on the functional model with additional systematic parameters induced by the compatibility and interoperability problems among different GNSS systems. The third type of generalised DOP is defined based on Bayesian estimation in which the a priori information of the model parameters is taken into account. This is suitable for evaluating the precision of kinematic positioning or navigation. Different types of generalised DOPs are suitable for different PNT scenarios and an example for the calculation of these DOPs for multi-GNSS systems including GPS, GLONASS, Compass and Galileo is given. New observation equations of Compass and GLONASS that may contain additional parameters for interoperability are specifically investigated. It shows that if the interoperability of multi-GNSS is not fulfilled, the increased number of satellites will not significantly reduce the generalised DOP value. Furthermore, the outlying measurements will not change the original DOP, but will change the first type of generalised DOP which includes a robust error IF. A priori information of the model parameters will also reduce the DOP.

Necessary and sufficient conditions of the rendezvous between a single spacecraft and three non-coplanar Walker constellation satellites

The probability of the rendezvous between a single spacecraft and three non-coplanar constellation satellites is studied, and the necessary and sufficient conditions of the rendezvous without orbital maneuver are deduced. The rendezvous orbit design can be transformed into the patching of two spacecraft orbits, either of which can achieve the rendezvous with two satellites. Firstly, due to the precious quality of spherical geometry, the unique existence of the rendezvous orbit for two constellation satellites is proved. Then, according to the difference between equispaced and non-equispaced orbital planes of three satellites, the necessary and sufficient conditions are given respectively, and the calculating method of the spacecraft orbit is proposed. At last, the constraint conditions between two different rendezvous orbits is derived, while the relative position of two groups of objects are under specific distribution. The results can be applied to the rendezvous between a single spacecraft and multiple constellation satellites without orbital maneuver.

A Multimodal Constellation Model for Object Image Classification

We present an efficient method for object image classification. The method is an extention of the constellation model, which is a part-based model. Generally, constellation model has two weak points. (1) It is essentially a unimodal model which is unsuitable to be applied for categories with many types of appearances. (2) The probability function that represents the constellation model requires a high calculation cost.We introduced multimodalization and speed-up technique to the constellation model to overcome these weak points. The proposed model consists of multiple subordinate constellation models so that diverse types of appearances of an object category could be described by each of them, leading to the increase of description accuracy and consequently, improvement of the classification performance. In this paper, we present how to describe each type of appearance as a subordinate constellationmodel without any prior knowledge regarding the types of appearances, and also the implementation of the extended model's learning in realistic time. In experiments, we confirmed the effectiveness of the proposedmodel by comparison to methods using BoF, and also that the model learning could be realized in realistic time.

Design criterion and construction methods for partially coherent multiple antenna constellations

We consider multiple-antenna communication systems in Rayleigh fading channel, where the transmitter does not know the channel coefficients and the receiver has only an estimate of them. We further assume that the transmitter and receiver know the statistics of the estimation error. We refer to this system as partially coherent system, for which we derive the expressions for the optimal detector and study the constellation design problem. Since the Chernoff bound on pairwise error probability of the partially coherent systems appears to be intractable, we use Stein's Lemma to propose a design criterion based on Kullback-Leibler (KL) distance between conditional distributions. Using the KL-based design criterion, we construct constellations for multiple-antenna systems which can be demodulated in the presence of channel estimation errors. The proposed constellations are multi-level, with multi-dimensional spherical constellations at each level. We show that these new constellations provide significant performance improvement over the conventional single-antenna PSK and QAM constellations, and multiple-antenna techniques such as Bell Lab's Space-Time (BLAST) architecture and orthogonal transmit diversity (OTD) schemes, when the estimation variance is comparable to the reciprocal of the signal-to-noise ratio.

FOUR NEW STELLAR DEBRIS STREAMS IN THE GALACTIC HALO

We report on the detection of four new stellar debris streams and a new dwarf galaxy candidate in the Sloan Digital Sky Survey. Three of the streams, ranging between 3 and 15 kpc in distance and spanning between 37 and 84 degrees on the sky, are very narrow and are most probably tidal streams originating in extant or disrupted globular clusters. The fourth stream is much broader, roughly 45 kpc distant, at least 53 degrees in length, and is most likely the tidal debris from a dwarf galaxy. As the streams each span multiple constellations, we extend tradition and designate them the Acheron, Cocytos, Lethe, and Styx streams. At the same distance and apparently embedded in the Styx stream is a ~1 kpc-wide concentration of stars with a similar color-magnitude distribution which we designate Bootes III. Given its very low surface density, its location within the stream, and its apparently disturbed morphology, we argue that Bootes III may be the progenitor of Styx and in possibly the final throes of tidal dissolution. While the current data do not permit strong constraints, preliminary orbit estimates for the streams do not point to any likely progenitors among the known globular clusters and dwarf galaxies.

Very fast detection for rate-2 quasi-orthogonal STBCs

For an important and standard rate-two quasi-orthogonal space-time block code, we propose a very fast detection scheme which achieves a wide range of tradeoff between performance and complexity. In the proposed scheme, exploiting the special quasi-orthogonal structure of the code, we efficiently obtain multiple candidate constellation points around the maximum likelihood (ML) point. Furthermore, we develop a very fast sorting method for the multiple candidate points to further improve the detection speed. Numerical results demonstrate that the proposed scheme can perform very close to the maximum likelihood detection at an extremely low complexity.

Threshold-Based Substream Selection for Closed-Loop Spatial Multiplexing

We propose a low-complexity closed-loop spatial multiplexing method with limited feedback over multi-input-multi-output (MIMO) fading channels. The transmit adaptation is simply performed by selecting transmit antennas (or substreams) by comparing their signal-to-noise ratios to a given threshold with a fixed nonadaptive constellation and fixed transmit power per substream. We analyze the performance of the proposed system by deriving closed-form expressions for spectral efficiency, average transmit power, and bit error rate (BER). Depending on practical system design constraints, the threshold is chosen to maximize the spectral efficiency (or minimize the average BER) subject to average transmit power and average BER (or spectral efficiency) constraints, respectively. We present numerical and Monte Carlo simulation results that validate our analysis. Compared to open-loop spatial multiplexing and other approaches that select the best antenna subset in spatial multiplexing, the numerical results illustrate that the proposed technique obtains significant power gains for the same BER and spectral efficiency. We also provide numerical results that show improvement over rate-adaptive orthogonal space-time block coding, which requires highly complex constellation adaptation. We analyze the impact of feedback delay using analytical and Monte Carlo approaches. The proposed approach is arguably the simplest possible adaptive spatial multiplexing system from an implementation point of view. However, our approach and analysis can be extended to other systems using multiple constellations and power levels.

Regionalized Lunar South Pole Surface Navigation System Analysis

Apollo missions utilized Earth‐based assets for navigation, since the landings took place at lunar locations in constant view from the Earth. The new exploration campaign to the lunar South Pole region will have limited Earth visibility, but the extent to which a navigation system comprised solely of Earth‐based tracking stations will provide adequate navigation solutions in this region is unknown. This article presents a dilution‐of‐precision‐(DoP‐) based stationary surface navigation analysis of the performance of multiple lunar satellite constellations, Earth‐based deep space network assets, and combinations thereof. Results show that kinematic and integrated solutions cannot be provided by the Earth‐based deep space network stations. Also, the surface stationary navigation system needs to be operated as a two‐way navigation system, or as a one‐way navigation system with local terrain information, while integrating the position solution over a short duration of time with navigation signals being provided by a lunar satellite constellation.

Nondiagonal MIMO QFT Controller Design for Darwin-Type Spacecraft With Large Flimsy Appendages

This paper deals with the design of robust control strategies to govern the position and attitude of a Darwin-type spacecraft with large flexible appendages. The satellite is one of the flyers of a multiple spacecraft constellation for a future ESA mission. It presents a 6×6 high order multiple-input–multiple-output (MIMO) model with large uncertainty and loop interactions introduced by the flexible modes of the low-stiffness appendages. The scientific objectives of the satellite require very demanding control specifications for position and attitude accuracy, high disturbance rejection, loop-coupling attenuation, and low controller order. The paper demonstrates the feasibility of a sequential nondiagonal MIMO quantitative feedback theory (QFT) strategy controlling the Darwin spacecraft and compares the results with H-infinity and sequential diagonal MIMO QFT designs.