A Direct Construction of Prime-Power-Length Zero-Correlation Zone Sequences for QS-CDMA System

In recent years, zero-correlation zone (ZCZ) sequences are being studied due to their significant applications in quasi-synchronous code division multiple access (QS-CDMA) systems and other wireless communication domains. However, the lengths of most existing ZCZ sequences are limited, and their parameters are not flexible, which are leading to practical limitations in their use in QS-CDMA and other communication systems. The current study proposes a direct construction of ZCZ sequences of prime-power length with flexible parameters by using multivariable functions. In the proposed construction, we first present a multivariable function to generate a vector with specific properties; this is further used to generate another class of multivariable functions to generate the desired $(p^t,(p-1)p^n,p^{n+t+1})$-ZCZ sequence set, where $p$ is a prime number, $t,n$ are positive integers, and $t\leq n$. The constructed ZCZ sequence set is optimal for the binary case and asymptotically optimal for the non-binary case by the \emph{Tang-Fan-Matsufuji} bound. Moreover, a relation between the second-order cosets of first-order generalized Reed-Muller code and the proposed ZCZ sequences is also established. The proposed construction of ZCZ sequences is compared with existing constructions, and it is observed that the parameters of this ZCZ sequence set are a generalization of that of in some existing works. Finally, the performance of the proposed ZCZ-based QS-CDMA system is compared with the Walsh-Hadamard and Gold code-based QS-CDMA system

New Constructions of Zero-Correlation Zone Sequences

In this paper, we propose three classes of systematic approaches for constructing zero correlation zone (ZCZ) sequence families. In most cases, these approaches are capable of generating sequence families that achieve the upper bounds on the family size ($K$) and the ZCZ width ($T$) for a given sequence period ($N$). Our approaches can produce various binary and polyphase ZCZ families with desired parameters $(N,K,T)$ and alphabet size. They also provide additional tradeoffs amongst the above four system parameters and are less constrained by the alphabet size. Furthermore, the constructed families have nested-like property that can be either decomposed or combined to constitute smaller or larger ZCZ sequence sets. We make detailed comparisons with related works and present some extended properties. For each approach, we provide examples to numerically illustrate the proposed construction procedure.Comment: 37 pages, submitted to IEEE Transactions on Information Theor

Near-Optimal Zero Correlation Zone Sequence Sets from Paraunitary Matrices

Zero correlation zone (ZCZ) sequence sets play an important role in interference-free quasi-synchronous code-division multiple access communications. In this paper, for the first time, we investigate the periodic correlation properties of polyphase sequences obtained from paraunitary (PU) matrices, which shows the inherent relationship between PU matrix and ZCZ sequence sets. Our investigation suggests that any arbitrary PU matrix can produce ZCZ sequence sets by controlling its expanded form. The key idea is to impose certain restrictions on the expanded forms of the PU matrices to enable precise computation of the periodic correlation functions of the constructed sequences. We show that our proposed construction leads to near-optimal ZCZ sequence sets with regard to the ZCZ set size upper bound

Demographic History and Natural Selection Shape Patterns of Deleterious Mutation Load and Barriers to Introgression across Populus Genome

Hybridization and resulting introgression are important processes shaping the tree of life and appear to be far more common than previously thought. However, how the genome evolution was shaped by various genetic and evolutionary forces after hybridization remains unresolved. Here we used whole-genome resequencing data of 227 individuals from multiple widespread Populus species to characterize their contemporary patterns of hybridization and to quantify genomic signatures of past introgression. We observe a high frequency of contemporary hybridization and confirm that multiple previously ambiguous species are in fact F-1 hybrids. Seven species were identified, which experienced different demographic histories that resulted in strikingly varied efficacy of selection and burdens of deleterious mutations. Frequent past introgression has been found to be a pervasive feature throughout the speciation of these Populus species. The retained introgressed regions, more generally, tend to contain reduced genetic load and to be located in regions of high recombination. We also find that in pairs of species with substantial differences in effective population size, introgressed regions are inferred to have undergone selective sweeps at greater than expected frequencies in the species with lower effective population size, suggesting that introgression likely have higher potential to provide beneficial variation for species with small populations. Our results, therefore, illustrate that demography and recombination have interplayed with both positive and negative selection in determining the genomic evolution after hybridization

Shuttle Ku-band signal design study

Carrier synchronization and data demodulation of Unbalanced Quadriphase Shift Keyed (UQPSK) Shuttle communications' signals by optimum and suboptimum methods are discussed. The problem of analyzing carrier reconstruction techniques for unbalanced QPSK signal formats is addressed. An evaluation of the demodulation approach of the Ku-Band Shuttle return link for UQPSK when the I-Q channel power ratio is large is carried out. The effects that Shuttle rocket motor plumes have on the RF communications are determined also. The effect of data asymmetry on bit error probability is discussed

Unlocking paleo-environmental information from Early Cretaceous shelf sediments in the Helvetic Alps: stratigraphy is the key!

The northern alpine Helvetic thrust-and-fold belt includes an Early Cretaceous shallow-water carbonate succession, which was part of an extensive carbonate platform rimming the northern Tethyan margin. The structural architecture of the Helvetic zone allows for the palinspastic reconstruction of proximal-distal transects across the former platform into the outer-shelf realm for distances surpassing 80km. The Early Cretaceous platform sediments preserved therein provide, therefore, excellent insight into the spatial and temporal evolution of this platform. Furthermore, the presence of ammonites in marker horizons within the Helvetic succession is key to unprecedented time control. During the life span of the Helvetic platform, carbonate build up and build out occurred along two distinct pathways: we discern between a mode including oligotrophic photozoan communities (latest Tithonian - Late Berriasian; Late Barremian; Early Aptian) and a mode dominated by mesotrophic heterozoan communities (Valanginian - Early Barremian; earliest Aptian; late Early Aptian - Late Aptian). The heterozoan mode was frequently interrupted by incipient platform drowning episodes, which materialized either in an important erosive hiatus, or in the deposition of highly condensed, glauconiteand phosphate-rich intervals (Early Valanginian - Early Hauterivian; late Early - early Late Hauterivian; latest Hauterivian - latest Early Barremian; middle Late Barremian; late Early Aptian - early Late Aptian; and latest Aptian - Early Albian). The photozoan mode is interpreted as essentially oligotrophic, whereas the heterozoan and drowning phases were associated with the input of coarser-grained detrital sediments and a correspondingly increased nutrient load, which were both the consequence of intensified chemical weathering on the continent due to warmer and more humid climate conditions. Their onset is signaled by increases in oceanic phosphorus burial rates and major positive excursions in the stable carbon isotope record. Oceanic anoxic episodes occurred during these latter phases. The northern Tethyan platform was not only controlled by climatic, environmental and paleoceanographic change, but changes in platform morphology and the composition of carbonate-producing benthic communities also influenced the quality and quantity of dissolved and particulate material exported into adjacent basin

Hierarchy Based Construction of Signature Matrices for Simplified Decoding in Overloaded CDMA

The overloaded CDMA system, as the solution to the capacity limit of its conventional counterpart, has drawn frequent interest of the researchers in the past. While there exists numerous proposals on the construction of uniquely decodable (UD) signature matrices for overloaded CDMA system with very high value of overloading factor, most of them lag the efficient multiuser detector (MUD) for noisy transmission. Here, by efficient, we imply the MUD to have acceptable BER performance and simplified in design. Whereas the lack of efficiency of several MUDs is primarily due to the impact of excess level of multiple access interference (MAI) because of the rise in the number of active users, its random nature prohibits its accurate estimation and elimination. Under such constraints, if the signature matrices can be intelligently constructed so as to generate a defined and controlled pattern (hierarchy) of MAI so that the designed MUD will exploit the knowledge of this hierarchy to remove the MAI completely and attain better error performance at much lower cost of complexity. We consider this as the motivation for research in this thesis. First, we propose the ternary signature matrix with orthogonal subsets (TSMOS), where the matrix with index-k comprises of k orthogonal subsets with each having different number signatures, and all subsets besides the first (largest) one are of ternary type. The correlation (interference) pattern among the signatures is mapped into a twin tree hierarchy, which is further leveraged to design a simplified MUD using the linear decoding blocks like matched filter (MF) to provide errorfree and better error performance for noiseless and noisy transmission respectively. Next, we generalize the construction of TSMOS to multiple structures i.e.; Type I, Type II, Type III and mixed versions and reveal the complementary feature of 50% signatures of the largest (binary) subset that further results in their optimality. Further, we propose the non-ternary version of SMOS (called as 2k-SMOS), where the binary alphabets in each of the k subsets are different from each other. With vii no complementary feature, 50% signatures of its largest subset are also found to be optimal. The superiority of 2k-SMOS over TSMOS is also verified for an overloading capacity of 150%. Next, we propose and discuss the hybrid SMOS (HSMOS), where the subsets from TSMOS and 2k-SMOS are used as the constituents to produce multiple SMOS structures, of which TSMOS and 2k-SMOS are treated as the special cases. For better understanding of the features of the whole family of SMOS (with an overloading capacity of 200%), the gradual change in the twin tree hierarchy and BER performance of the left and right child of the individual subsets are studied. Similar to SMOS, we also introduce the hierarchy based low density signature (HLDS) matrix, where any UD matrix satisfying particular criterion can be considered as the basis set. For hadamard matrix as the basis set, we design a MUD that uses the MF to implement the decision vector search (DVS) algorithm, which is meant to exploit the advantageous hierarchy of constellation of the transmitted vector to offer errorfree decoding. For noisy channel, the marginal degradation in the level of BER of the MUD (DVS) as compared to the optimum joint maximum likelihood decoder (MLD) is worthy to be overlooked when compared with the significant gain achieved in terms of complexity. For the smallest dimension of the hadamard matrix as the basis, the MUD is further simplified to offer recovery using a comparison driven decision making algorithm, also known as comparison aided decoding (CAD). Despite simplicity, the error performance of the MUD (CAD) is observed to be very close to that of MUD (DVS)

Optimization Strategies for Spatio-temporal Groundwater Dynamics Monitoring

Räumlich kontinuierliche Daten sind in der Hydrogeologie für die wissenschaftliche Forschung, die Risikobewertung und wasserwirtschaftliche Entscheidungsprozesse von wesentlicher Bedeutung. Die meisten dieser Informationen werden allerdings nur punktuell durch Messungen an Grundwassermessstellen erhoben und anschließend regionalisiert. Die Vorhersagegenauigkeit dieser räumlich interpolierten Daten, die in der Regel die Grundlage für weitere Berechnungen und Entscheidungen bilden, ist stark abhängig von der Konzipierung des Grundwassermessnetzes, d.h. von der räumlichen Verteilung und Dichte der Grundwassermessstellen, der Beprobungshäufigkeit, dem Interpolationsverfahren sowie dem Wechselspiel zwischen diesen Faktoren. Daraus ergibt sich ein erhebliches Optimierungspotenzial hinsichtlich des Grundwassermessnetzes und der Regionalisierungstechnik. Geeignetes Grundwassermessnetze sind daher wichtige Instrumente für die nachhaltige Bewirtschaftung und für den Schutz der Grundwasserressourcen. Sie bieten Zugangspunkte für die Überwachung von Grundwasserständen und -proben und ermöglichen so einen Einblick in die Grundwasserverhältnisse. Die Kombination aus hohen Erschließungskosten und einer verhältnismäßig geringen räumlichen Repräsentativität der Brunnen aufgrund der hydrogeologischen Heterogenität machen die Konzeption eines geeigneten Überwachungsnetzes zu einer großen Herausforderung. Diese Arbeit beschäftigt sich mit Techniken zum verbesserten Verständnis der Grundwasserdynamik durch (i) räumliche und (ii) räumliche-zeitliche Optimierung von Grundwasserstands Messnetzen und (iii) verbesserter räumlichere Vorhersage der an diesen Überwachungsbrunnen gewonnenen Daten unter Verwendung von Interpolationstechniken. Zu diesem Zweck wurde im ersten Teil dieser Arbeit eine umfassende Untersuchung der meistgenutzten deterministischen und geostatistischen, uni- und multivariaten Interpolationstechniken für die Erstellung von Grundwassergleichenplänen in einem Untersuchungsgebiet durchgeführt, das durch eine komplexe Interaktion zwischen Karst, einem alluvialen Grundwasserleiter und gering durchlässigen Schichten der alpinen Molasse gekennzeichnet ist. Die untersuchten Methoden wurden durch globale Kreuzvalidierung und öko-hydrogeologische Informationen an Karstquellen, Feuchtgebieten, Oberflächengewässern und Profilschnitten bewertet. Der mögliche Effekt der Methodenwahl auf die weitere Berechnung wurde durch Abschätzung der Austauschprozesse zwischen Karst- und Alluvialgrundwasserleiter auf Basis der geschätzten Potentialunterschiede durchgeführt. Die Ergebnisse zeigen, dass die Verfahrenswahl, insbesondere bei unzureichendem Überwachungskonzept, drastische Auswirkungen auf die nachfolgenden Berechnungen haben kann. Die Studie hat ergeben, dass geostatistische oder Kriging Interpolationsmethoden den deterministischen Interpolationsmethoden überlegen sind. Bei dürftiger Grundwasserdatenlage kann das Co-Kriging mit räumlich kreuzkorrelierten Sekundärvariablen (z. B. Höhenlage, Flusspegel), die häufiger erfasst werden, wertvolle Informationen über die Primärvariable bereitstellen und so die Varianz des Schätzfehlers verringern. Im zweiten Teil dieser Arbeit wurden räumliche Monitoringkonzepte mit unterschiedlichen Messdichten an numerisch modellierter Grundwasseroberflächen mit verschiedenen Skalen und Dynamiken untersucht. Ziel war es, Einblicke in geeignete Monitoringansatze für eine verlässliche räumliche Abschätzung des Grundwasserspiegels zu gewinnen und eine Überwachungsdichte abzuleiten, bei der ein angemessenes Information/Kosten-Verhältnis erreicht wird. Die Interpolationsergebnisse wurden mit globaler Kreuzvalidierung und dem tatsächlichen räumlichen Fehler evaluiert, der anhand der numerischen Modellflächen als A-priori-Referenz errechnet wurde. Überwachungsnetze mit einer regelmäßigen Gitteranordnung boten zwar genaueste räumliche Vorhersagen für das betrachtete Dichtespektrum, sind jedoch aufgrund ihrer Nachteile, wie der mangelnden Erweiterungsfähigkeit, tendenziell ungeeignet. Eine vergleichbar gute Leistung wurde erzielt, wenn der maximale Vorhersage-Standardfehler als Auswahlkriterium für zusätzliche Brunnen für bestehende Messnetze verwendet wurde. In dieser Studie wurde außerdem eine neuartige Optimierungsstrategie für Überwachungsnetze angewandt, die auf mathematischen Quasi-Zufallsfolgen basiert. Der Ansatz liefert ebenfalls überzeugende Ergebnisse und bietet mehrere Vorteile. Er bedarf keinerlei Vorkenntnisse über den Grundwasserleiter durch vorhandene Brunnen und es werden unabhängig von den Ausbaustufen reproduzierbare räumliche Anordnungen erzielt. Im dritten Teil wurde ein datengesteuerter Sparse-Sensing-Algorithmus-Ansatz zur Auswahl von spärlichen Sensorpositionen unter Nutzung von Techniken zur Dimensionsreduktion untersucht und für die zeitliche und räumliche Optimierung eines bestehenden Grundwasserstandsmessnetzes im Oberrheingraben adaptiert. Die Optimierung erfolgt mit einem greedy search (QR)-Algorithmus, der die Überwachungsbrunnen nach ihrem Informationsgehalt über Aquifer-Dynamik selektiert und einordnet. Als Eingangsdaten wurden langjährige Ganglinien-Aufzeichnungen verwendet, um repräsentative Messstellen oder Messstellen mit redundantem oder niedrigem Informationsgehalt zu bestimmen. Des Weiteren wurde eine Optimierung auf der Grundlage regionalisierter, wöchentlicher Grundwassergleichenkarten durchgeführt, um mögliche geeignete Standorte für zusätzliche Messstellen zu identifizieren. Die Suche wurde durch eine räumliche Kostenfunktion gelenkt, bei der weniger geeignete Standorte abgewertet wurden. Der untersuchte Ansatz hat sich als potenziell wertvolles Instrument für die Optimierung der Brunnenanzahl und deren Standorte, für die Reduzierung und den Ausbau des Netzes aber auch für eine kombinierte Nutzung beider Möglichkeiten erwiesen

Signal Processing and Learning for Next Generation Multiple Access in 6G

Wireless communication systems to date primarily rely on the orthogonality of resources to facilitate the design and implementation, from user access to data transmission. Emerging applications and scenarios in the sixth generation (6G) wireless systems will require massive connectivity and transmission of a deluge of data, which calls for more flexibility in the design concept that goes beyond orthogonality. Furthermore, recent advances in signal processing and learning have attracted considerable attention, as they provide promising approaches to various complex and previously intractable problems of signal processing in many fields. This article provides an overview of research efforts to date in the field of signal processing and learning for next-generation multiple access, with an emphasis on massive random access and non-orthogonal multiple access. The promising interplay with new technologies and the challenges in learning-based NGMA are discussed