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The ambiguity-resolved detector: a detector for the mixed-integer GNSS model
In this contribution, we introduce the ambiguity-resolved (AR) detector and study its distributional characteristics. The AR-detector is a new detector that lies in between the commonly used ambiguity-float (AF) and ambiguity-known (AK) detectors. As the ambiguity vector can seldomly be known completely, usage of the AK-detector is questionable as reliance on its distributional properties will then generally be incorrect. The AR-detector resolves the shortcomings of the AK-detector by treating the ambiguities as unknown integers. We show how the detector improves upon the AF-detector, and we demonstrate that the, for ambiguity-resolved parameter estimation, commonly required extreme success rates can be relaxed for detection, thus showing that improved model validation is also possible with smaller success rates. As such, the AR-detector is designed to work for mixed-integer GNSS models.
Journal Article
Algorithm for the Weak Target Joint Detection and Ambiguity Resolution Based on Ambiguity Matrix
The looking-down mode of space airship bistatic radars faces complex sea–land clutter, and the mode of wide-range surveillance and the over-sight detection of the satellite platform generates a low SNR and range–Doppler ambiguity. The method traditionally used involves the transmission of multiple Pulse Repetition Frequencies (PRFs) and correlating them to solve the ambiguity. However, with a low SNR, the traditional disambiguation fails due to the large number of false alarms and target omissions. In order to solve this problem, a new algorithm for multi-target joint detection and range–Doppler disambiguation based on an ambiguity matrix is presented. Firstly, all possible state values corresponding to the ambiguous sequence are filled into the ambiguity matrix one by one. Secondly, the state values in the matrix cell are divided into several groups of subsequences according to the PRF. By disambiguating multiple sets of subsequences, performing subsequence fusion, and then undertaking point aggregation, the targets can be effectively detected in scenarios with a strong clutter rate, the false alarms can be suppressed, and the disambiguation of the range and Doppler is completed. The simulation shows that the proposed algorithm has the strong ability to detect targets and perform ambiguity resolution in the scenario of a multi-target and multi-false alarm.
Journal Article
Imagined borders/lived ambiguity : intersections of repression and resistance
Imagined Borders / Lived Ambiguity: Intersections of Repression and Resistance examines the theoretical versatility of the concept of \"borders.\" The impulse to categorize, while present from antiquity in Western culture, has increased in intensity since the advent of the modern age with its corresponding political rise in the ideology of the sovereign nation-state. While immigration is the common mental image Westerners have when discussing borders, immigration is only the tip of the iceberg for this book. The belief in mutually exclusive, clear, and concrete categories creates large swathes of exceptions where people live ambiguous lives nationally, racially, sexually, ethnically, and in terms of gender.Identity is discussed in the book through the lens of borders and ambiguity. The fervor over categorization, best embodied in recent political history by the Trump administration in the United States, is both a desire to identify and control \"dangerous\" populations, but also creates the very ambiguity categorization is intended to alleviate. The volume weaves together discussions on the subjective meaning-making in ambiguity, policies that create ambiguity, historical creations of ambiguity that persist to the present, and theoretical considerations on the relationship between borders and ambiguity.
Book
Phase ambiguity mitigation for per-cell codebookbased limited feedback coordinated multi-point transmission systems
Limited feedback techniques, that employ codebook-based quantisation, are used in coordinated multi-point (CoMP) transmission to convey the channel direction information between the mobile user and each base station in the cooperative set and also among the cooperating base stations. However, unlike single-cell multiple-user multiple input multiple output (MU-MIMO) systems, CoMP systems face additional challenges in this codebook design. Among these challenges are the huge feedback overhead and the need for dynamic codebook size. These problems are solved when CoMP uses the so-called per-cell codebook, in which the channel to each cell is quantised separately. However, this results in a further problem, that is having random phase values between the quantised per-cell channels of the same user. In this study, the phase ambiguity problem is explained and its effect on performance degradation is quantified. A new quantisation technique is proposed where the quantisation of each of the real and the imaginary parts is performed independently using the same real codebook. This novel solution prevents the phase ambiguity problem instead of trying to mitigate its effects, in addition to simplifying the codebook design. The proposed quantisation technique outperforms two recently introduced solutions in the literature. The first solution is to quantise phase ambiguity as part of channel state information (CSI), whereas the other avoids phase ambiguity by an iterative selection procedure. Mathematical validations and simulations are provided to verify these findings. [PUBLICATION ABSTRACT]
Journal Article
Ambiguity : language and communication
This volume uncovers a great mystery about language: why can we communicate so effectively despite the fact that ambiguity is pervasive? Conversely, how do speakers use ambiguity to achieve a specific goal? Answers to these questions are provided from different fields: (psycho)linguistics, literary criticism, rhetoric, theology, media studies, [and] law.
Book
A sequential ambiguity selection strategy for partial ambiguity resolution during RTK positioning in urban areas
Usually, it is difficult to implement integer ambiguity resolution within a short amount of time for GNSS positioning in urban areas due to the contamination of non-line-of-sight signals and multipath. This study proposes a sequential ambiguity selection strategy for partial ambiguity resolution. First, the ambiguities are selected based on the filtered residuals of the phase and code measurements. In addition, the elevation angle and decorrelated variances are used as the metrics for selecting ambiguity subsets. Two kinematic experiments are carried out in urban areas to evaluate the performance of the strategy. Among the three independent strategies, the first one performs better than the others, as the dependency of observation quality on the elevation angle is low and the decorrelated variances are prone to be contaminated by biased ambiguities. When the proposed sequential ambiguity selection strategy is used, the percentage of correctly fixed epochs is increased by approximately 10–20%. The RMS of N/E/U is improved from the decimeter level (for full ambiguity resolution) to the centimeter level. The improvement is more obvious in the obstructed area and during the re-initialization phase.
Journal Article
A new GLONASS FDMA model
We introduce a new formulation of the double-differenced GLONASS FDMA model. It closely resembles that of CDMA-based systems and it guarantees the estimability of the newly defined GLONASS ambiguities. The formulation is made possible because of our defining new concept of integer-estimability and the analytical construction of a special integer matrix canonical decomposition. As a result, an easy-to-compute new design matrix is created that automatically establishes the integer-estimability of the ambiguities. The presented model is generally applicable, and its close resemblance to its CDMA-counterparts implies that available CDMA-based GNSS software is easily modified and that existing methods of integer ambiguity resolution can be directly applied. Also, because of their similar structure, many of the available CDMA results with corresponding insights can now be directly translated to the GLONASS case. We make use of this property to provide insight into the ambiguity resolution capabilities of the model and to analyze the characteristics of the GLONASS ambiguity dilution of precision.
Journal Article