TWO GENERALIZATIONS OF SKEW-SYMMETRIC SEQUENCES WITH ODD LENGTHS

The signals, exploited by the radar sensor networks and remote control systems, have to provide simultaneously high range resolution and ability to work stable in a hostile radio electronic environment. An effective approach for satisfying of these requirements is the frequent change of many different signals, which autocorrelation functions have small sidelobes. Accounting this situation in the paper the generalizations of the skew-symmetric sequences with odd lengths, which are phase manipulated signals, possessing high autocorrelation merit factor, are explored. As a result, two methods for synthesis of infinite families of phase manipulated signals with good autocorrelation properties are substantiated

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

Doppler Shift Tolerance of Typical Pseudorandom Binary Sequences in PMCW Radar

In the context of all-digital radar systems, phase-modulated continuous wave (PMCW) based on pseudorandom binary sequences (PRBSs) appears to be a prominent candidate modulation scheme for applications such as autonomous driving. Among the reasons for its candidacy are its simplified transmitter architecture and lower linearity requirements (e.g., compared to orthogonal-frequency division multiplexing radars), as well as its high velocity unambiguity and multiple-input multiple-output operation capability, all of which are characteristic of digital radars. For appropriate operation of a PMCW radar, choosing a PRBS whose periodic autocorrelation function (PACF) has low sidelobes and high robustness to Doppler shifts is paramount. In this sense, this article performs an analysis of Doppler shift tolerance of the PACFs of typically adopted PRBSs in PMCW radar systems supported by simulation and measurement results. To accurately measure the Doppler-shift-induced degradation of PACFs, peak power loss ratio (PPLR), peak sidelobe level ratio (PSLR), and integrated-sidelobe level ratio (ISLR) were used as metrics. Furthermore, to account for effects on targets whose ranges are not multiples of the range resolution, oversampled PACFs are analyzed

HpGAN: Sequence Search with Generative Adversarial Networks

Sequences play an important role in many engineering applications and systems. Searching sequences with desired properties has long been an interesting but also challenging research topic. This article proposes a novel method, called HpGAN, to search desired sequences algorithmically using generative adversarial networks (GAN). HpGAN is based on the idea of zero-sum game to train a generative model, which can generate sequences with characteristics similar to the training sequences. In HpGAN, we design the Hopfield network as an encoder to avoid the limitations of GAN in generating discrete data. Compared with traditional sequence construction by algebraic tools, HpGAN is particularly suitable for intractable problems with complex objectives which prevent mathematical analysis. We demonstrate the search capabilities of HpGAN in two applications: 1) HpGAN successfully found many different mutually orthogonal complementary code sets (MOCCS) and optimal odd-length Z-complementary pairs (OB-ZCPs) which are not part of the training set. In the literature, both MOCSSs and OB-ZCPs have found wide applications in wireless communications. 2) HpGAN found new sequences which achieve four-times increase of signal-to-interference ratio--benchmarked against the well-known Legendre sequence--of a mismatched filter (MMF) estimator in pulse compression radar systems. These sequences outperform those found by AlphaSeq.Comment: 12 pages, 16 figure

Конструиране на булеви функции и цифрови последователности за криптологията и комуникациите

ИМИ-БАН, секция "Математически основи на информатиката", 2023 г., присъждане на образователна и научна степен "доктор" на Мирослав Маринов Димитров в професионално направление информатика и компютърни науки. [Dimitrov Miroslav Marinov; Димитров Мирослав Маринов

Low peak derivative sum of sines

This paper proposes a method to generate multisines signals with reduced peak derivative. This is done by adjusting the phases in the Fourier domain with Genetic Algorithm such that in the time domain the maximum absolute signal's derivative is minimized. The performance evaluation is made by comparing the method to signals with the same spectrum but with phase adjusted randomly. It will be shown for an audio test signal case study of a multisines signal comprising 2500 sines that a reduction of 42% with respect to the mean maximum peak derivative and 31% with respect to the minimum maximum peak derivative over 1 million random trials. The proposed method is contrasted with a low crest factor signal method. It is found that there is a positive correlation between peak amplitude and peak derivative when signals are generated with random phases. Moreover, the signals obtained by minimizing either the peak amplitude of the peak derivative had also good performances with respect to the non-optimized criterion

Time-domain multitone impedance measurement system for space applications

© 2022 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes,creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.This paper presents a time-domain methodology to measure the devices' live impedance at the frequency range between 30 Hz and 100 kHz. This measurement is a requirement for some space applications to ensure the stability between DC/DC converters and the onboard power. The methodology is based on a multitone excitation combined with current and voltage measurements performed with an oscilloscope. The experiments show that the measurement system obtains accurate results and offers new capabilities to deal with the drawbacks that traditional frequency-sweep instrumentation implies. The multitone approach injects signals at the entire frequency range simultaneously. Therefore, the measurement system is able to characterize time-varying and the nonlinear devices. The time-domain measurement system has been validated through different test cases achieving excellent results compared with the ones obtained using the reference impedance frequency-sweep approach.The project on which these results are based has received funding from the European Union's Horizon 2020 research and innovation programme under Marie Skłodowska-Curie grant agreement No. 801342 (TecniospringINDUSTRY) and the Government of Catalonia's Agency for Business Competitiveness (ACCIÓ). This work was supported by the Spanish “Agencia Estatal de Investigación” under project PID2019-106120RBC31/AEI/10.13039/501100011033.Peer ReviewedPostprint (author's final draft