Design of sequences with good correlation properties

This thesis is dedicated to exploring sequences with good correlation properties. Periodic sequences with desirable correlation properties have numerous applications in communications. Ideally, one would like to have a set of sequences whose out-of-phase auto-correlation magnitudes and cross-correlation magnitudes are very small, preferably zero. However, theoretical bounds show that the maximum magnitudes of auto-correlation and cross-correlation of a sequence set are mutually constrained, i.e., if a set of sequences possesses good auto-correlation properties, then the cross-correlation properties are not good and vice versa. The design of sequence sets that achieve those theoretical bounds is therefore of great interest. In addition, instead of pursuing the least possible correlation values within an entire period, it is also interesting to investigate families of sequences with ideal correlation in a smaller zone around the origin. Such sequences are referred to as sequences with zero correlation zone or ZCZ sequences, which have been extensively studied due to their applications in 4G LTE and 5G NR systems, as well as quasi-synchronous code-division multiple-access communication systems. Paper I and a part of Paper II aim to construct sequence sets with low correlation within a whole period. Paper I presents a construction of sequence sets that meets the Sarwate bound. The construction builds a connection between generalised Frank sequences and combinatorial objects, circular Florentine arrays. The size of the sequence sets is determined by the existence of circular Florentine arrays of some order. Paper II further connects circular Florentine arrays to a unified construction of perfect polyphase sequences, which include generalised Frank sequences as a special case. The size of a sequence set that meets the Sarwate bound, depends on a divisor of the period of the employed sequences, as well as the existence of circular Florentine arrays. Paper III-VI and a part of Paper II are devoted to ZCZ sequences. Papers II and III propose infinite families of optimal ZCZ sequence sets with respect to some bound, which are used to eliminate interference within a single cell in a cellular network. Papers V, VI and a part of Paper II focus on constructions of multiple optimal ZCZ sequence sets with favorable inter-set cross-correlation, which can be used in multi-user communication environments to minimize inter-cell interference. In particular, Paper~II employs circular Florentine arrays and improves the number of the optimal ZCZ sequence sets with optimal inter-set cross-correlation property in some cases.Doktorgradsavhandlin

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

Journal of Telecommunications and Information Technology, 2003, nr 2

kwartalni

Monitoring system for long-distance pipelines subject to destructive attack

In an era of terrorism, it is important to protect critical pipeline infrastructure, especially in countries where life is strongly dependent on water and the economy on oil and gas. Structural health monitoring (SHM) using acoustic waves is one of the common solutions. However, considerable prior work has shown that pipes are cylindrical acoustic waveguides that support many dispersive, lossy modes; only the torsional T(0, 1) mode has zero dispersion. Although suitable transducers have been developed, these typically excite several modes, and even if they do not, bends and supports induce mode conversion. Moreover, the high-power transducers that could in principle be used to overcome noise and attenuation in long distance pipes present an obvious safety hazard with volatile products, making it difficult to distinguish signals and extract pipeline status information. The problem worsens as the pipe diameter increases or as the frequency rises (due to the increasing number of modes), if the pipe is buried (due to rising attenuation), or if the pipe carries a flowing product (because of additional acoustic noise). Any system is therefore likely to be short-range. This research proposes the use of distributed active sensor network to monitor long-range pipelines, by verifying continuity and sensing small disturbances. A 4-element cuboid Electromagnetic Acoustic Transducer (EMAT) is used to excite the longitudinal L(0,1) mode. Although the EMAT also excites other slower modes, long distance propagation allows their effects to be separated. Correlation detection is exploited to enhance signal-to-noise ratio (SNR), and code division multiplexing access (CDMA) is used to distinguish between nodes in a multi-node system. An extensive numerical search for multiphase quasi-orthogonal codes for different user numbers is conducted. The results suggest that side lobes degrade performance even with the highest possible discrimination factor. Golay complementary pairs (which can eliminate the side lobes completely, albeit at the price of a considerable reduction in speed) are therefore investigated as an alternative. Pipeline systems are first reviewed. Acoustic wave propagation is described using standard theory and a freeware modeling package. EMAT modeling is carried out by numerical calculation of electromagnetic fields. Signal propagation is investigated theoretically using a full system simulator that allows frequency-domain description of transducers, dispersion, multi-mode propagation, mode conversion and multiple reflections. Known codes for multiplexing are constructed using standard algorithms, and novel codes are discovered by an efficient directed search. Propagation of these codes in a dispersive system is simulated. Experiments are carried out using small, unburied air-filled copper pipes in a frequency range where the number of modes is small, and the attenuation and noise are low. Excellent agreement is obtained between theory and experiment. The propagation of pulses and multiplexed codes over distances up to 200 m are successfully demonstrated, and status changes introduced by removable reflectors are detected.Open Acces

Basement-Cover Relationships and Regional Structure in the Transtensional Orcadian Basin

Geological evidence suggests that the Orcadian Basin, a thick development of Devonian age continental facies, comprising alluvial, fluvial, lacustrine and aeolian deposits, is analogous to the Clair Group which developed in the smaller, offshore Clair Basin. Studies for the Clair Group to date have focussed on the predominantly fluvial-lacustrine rocks of the central Orcadian Basin in Caithness and Orkney. However, alternatives exist in Shetland and around the margins of the Orcadian Basin which are of a closer affinity to the predominantly fluvial-alluvial rocks of the Clair Group. Detailed field studies and structural analysis of basement-cover contacts and the overlying Devonian sedimentary sequences were undertaken in Shetland, Orkney and NE Scotland, in order to understand the scale, geometry and distribution of structures, and as an analogue to equivalent features in the subsurface, at sub-seismic to outcrop scales. This was supplemented by the integration of legacy and new multiscale data (topographic, bathymetric, geological and geophysical) and the production of photogrammetric 3D Virtual Outcrop Models. A diverse range of basement/cover relationships occurs both spatially and temporally in the basin, together with synchronous Middle Devonian syn-sedimentary faulting and growth folding, as observed on Foula. Thus, some folds interpreted as Permo-Carboniferous inversion structures may have instead initiated earlier, as Devonian growth folds. These folds, together with the large-scale structural geometries of the basins in Shetland are consistent with models of regional constrictional strain, related to sinistral transtension along the Walls Boundary and Great Glen Fault Zones during the Middle Devonian. Analysis of high-resolution bathymetric data from offshore Caithness/Orkney has provided new insights into the distribution and scale of structures in the Orcadian Basin that are poorly exposed onshore, with kilometre-scale folds and numerous faults and fracture zones being mapped for the first time. Provenance studies indicate that Foula and Melby in Western Shetland show a stronger affinity with the Clair Group and Orkney successions, suggesting a large, linked depositional system with Foula representing a transitional region located between the Clair and Orcadian basins. These findings suggest that the Devonian basins of Western Shetland and marginal areas of the Orcadian Basin are suitable analogues to the Clair Basin. Models of Devonian basin development used offshore should also consider the role of strike-slip tectonics and sinistral transtension during basin evolution

3C Seismic Interferometry at the Polymetallic Kylylahti Deposit, Outokumpu District, Finland

Non peer reviewe

New digital learning materials for teaching in geosciences

Non peer reviewe

Seismic mineral exploration at different scales in the Outokumpu Ore District, Eastern Finland

Non peer reviewe

COGITO-MIN seismic reflection profiling for mineral exploration in Polvijärvi, Finland

Non peer reviewe