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

Étude et évaluation de la consommation énergétique d'une balise ferroviaire fondée sur l'ULB et le retournement temporel.

In railway signaling, accurate and safe localization of trains is of paramount importance for the safe exploitation of railway networks. Therefore, train odometry has received considerable interest. Usually, train odometers manage different embarked sensors including wheel counters and Doppler radars that compute the position and the speed of the trains. However, as trains move, these proprioceptive sensors accumulate drifts and, as a consequence, train localization accuracy is compromised after several kilometers. In order to fix this drift problem, railway signaling uses beacons installed at ground, on the track, between the rails. Installed every several kilometers, they transmit absolute localization information to trains passing over them thus, bringing back locally the drifts to zero. These beacons constitute major components of railway signaling and also one of the very last equipment installed between the rails. Existing railway beacons are placed on the rails for two main reasons. First of all, since in these conditions the radio link between the train and the beacons remains very short, in the order of a few tens of centimeters, placing the beacons on the rails is very helpful to deliver an accurate local absolute localization to the train. Moreover using this very short radio communication range, while passing over them, trains can supply electrical energy to the beacons by magnetically coupling radiofrequency energy from the train to the beacon. This radiofrequency energy is detected and converted in DC power supply to feed the beacon electronics. This very short range leads to a satisfactory transfer of energy between train and beacon. As indicated previously, beacons can just be position indicators; however, they can also handle communication between grounds and trains using a peer to peer radio link. In this case, communication is only active when the train passes over the beacons, thus, the effective communication time is very short. As another major drawback of this particular implementation between the rails, track maintenance requires disassembling the beacons and then repositioning them safely and accurately.Dans un contexte où les ressources énergétiques sont moindres et la demande en termes de débit de communication est forte, il est intéressant de proposer des solutions techniques au niveau de la couche physique permettant d’optimiser la consommation énergétique de systèmes. Actuellement, pour une localisation précise et un transfert de données entre voie et trains efficace, la signalisation ferroviaire exploite des balises disposées entre les rails. La durée possible de la communication entre trains et balises s’avère très brève et n’est effective que lorsque le train passe juste au-dessus de la balise. Celle-ci reste en état de veille jusqu’à ce que le train la télé alimente lors de son passage. Le temps de communication utile entre le train et la balise s’établit à 3-4 ms pour un train roulant à 300 km/h. Par conséquent, plusieurs équipements consécutifs doivent être installés si l’on veut accroître la durée d’échange ou encore la quantité de données échangées. En outre, le fait d’émettre continument un puissant signal de télé alimentation radiofréquence non exploité depuis tous les trains en circulation, la difficulté de maintenance liée à la présence de cet équipement entre les rails, ainsi que la portée et donc la capacité de communication réduites des balises actuelles constituent autant de limitations que nous tentons de pallier avec ce nouvel équipement. Dès lors, nous développons une nouvelle génération de balise ferroviaire fondée sur un lien radiofréquence qui possède une portée atteignant quelques mètres, nettement plus importante que celle exploitable actuellement. Cette balise est également située en bord de voie et non entre les rails pour des questions de facilité de maintenance. Nous utilisons une technique de focalisation du signal émis depuis la balise vers l’antenne embarquée sur le train. Puisque la distance de communication balise au sol - interrogateur est portée à quelques mètres, la télé alimentation par couplage inductif actuelle n’est plus possible. Disposer d’une infrastructure centrale pour alimenter toutes les balises présentes sur le réseau n’est pas réaliste non plus. Une solution raisonnable et économe consiste à générer de l’énergie électrique basse tension localement en utilisant des énergies renouvelables (solaire, éolienne…), et en limitant le plus possible la consommation d’énergie de l’électronique de la balise. Dans cette optique, la contribution scientifique présentée consiste à développer et à optimiser, en termes d’énergie consommée, la couche physique de communication de cet équipement

Rich Words and Balanced Words

This thesis is mostly focused on palindromes. Palindromes have been studied extensively, in recent years, in the field of combinatorics on words.Our main focus is on rich words, also known as full words. These are words which have maximum number of distinct palindromes as factors.We shed some more light on these words and investigate certain restricted problems. Finite rich words are known to be extendable to infinite rich words. We study more closely how many different ways, and in which situations, rich words can be extended so that they remain rich.The defect of a ord is defined to be the number of palindromes the word is lacking.We will generalize the definition of defect with respect to extending the word to be infinite.The number of rich words, on an alphabet of size $n$, is given an upper and a lower bound. Hof, Knill and Simon presented (Commun. Math. Phys. 174, 1995) a well-known question whether all palindromic subshifts which are enerated by primitive substitutions arise from substitutions which are in class P. Over the years, this question has transformed a bit and is nowadays called the class P conjecture. The main point of the conjecture is to attempt to explain how an infinite word can contain infinitely many palindromes.We will prove a partial result of the conjecture. Rich square-free words are known to be finite (Pelantov\'a and Sarosta, Discrete Math. 313, 2013). We will give another proof for that result. Since they are finite, there exists a longest such word on an $n$-ary alphabet.We give an upper and a lower bound for the length of that word. We study also balanced words. Oliver Jenkinson proved (Discrete Math., Alg. and Appl. 1(4), 2009) that if we take the partial sum of the lexicographically ordered orbit of a binary word, then the balanced word gives the least partial sum. The balanced word also gives the largest product. We will show that, at the other extreme, there are the words of the form $0^{q-p}1^p$ ($p$ and $q$ are integers with $1\leq p<q$), which we call the most unbalanced words. They give the greatest partial sum and the smallest product.Tässä väitöskirjassa käsitellään pääasiassa palindromeja. Palindromeja on tutkittu viime vuosina runsaasti sanojen kombinatoriikassa.Suurin kiinnostuksen kohde tässä tutkielmassa on rikkaissa sanoissa. Nämä ovat sanoja joissa on maksimaalinen määrä erilaisia palindromeja tekijöinä.Näitä sanoja tutkitaan monesta eri näkökulmasta. Äärellisiä rikkaita sanoja voidaan tunnetusti jatkaa äärettömiksi rikkaiksi sanoiksi.Työssä tutkitaan tarkemmin sitä, miten monella tavalla ja missä eri tilanteissa rikkaita sanoja voidaan jatkaa siten, että ne pysyvät rikkaina.Sanan vajauksella tarkoitetaan puuttuvien palindromien lukumäärää.Vajauksen käsite yleistetään tapaukseen, jossa sanaa on jatkettava äärettömäksi sanaksi.Rikkaiden sanojen lukumäärälle annetaan myös ylä- ja alaraja. Hof, Knill ja Simon esittivät kysymyksen (Commun. Math. Phys. 174, 1995), saadaanko kaikki äärettömät sanat joissa on ääretön määrä palindromeja tekijöinä ja jotka ovat primitiivisen morfismin generoimia, morfismeista jotka kuuluvat luokkaan P. Nykyään tätä ongelmaa kutsutaan luokan P konjektuuriksi ja sen tarkoitus on saada selitys sille,millä tavalla äärettömässä sanassa voi olla tekijöinä äärettömän monta palindromia. Osittainen tulos tästä konjektuurista todistetaan. Rikkaiden neliövapaiden sanojen tiedetään olevan äärellisiä (Pelantov\'a ja Starosta, Discrete Math. 313, 2013). Tälle tulokselle annetaan uudenlainen todistus.Koska kyseiset sanat ovat äärellisiä, voidaan selvittää mikä niistä on pisin.Ylä- ja alaraja annetaan tällaisen pisimmän sanan pituudelle. Työssä tutkitaan myös tasapainotettuja sanoja.Tasapainotetut sanat antavat pienimmän osittaissumman binäärisille sanoille (Jenkinson, Discrete Math., Alg. and Appl. 1(4), 2009).Lisäksi ne antavat suurimman tulon.Muotoa $0^{q-p}1^p$ ($p$ ja $q$ ovat kokonaislukuja joille $1\leq p<q$) olevien sanojen todistetaan vastaavasti antavan suurimman osittaissumman ja pienimmän tulon.Ne muodostavat täten toisen ääripään tasapainotetuille sanoille, ja asettavat kaikki muut sanat näiden väliin.Siirretty Doriast

Dispersed concentration of high-tech jobs in the new economy : the paradox of new information and communication technologies

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Urban Studies and Planning, 2006.Includes bibliographical references (leaves 97-103).More high-tech firms are conducting their business over long distances due to the use of new information and communication technologies (ICT). However, regional scientists articulate that geographic proximity is still important, at least, to the high-tech industry and the knowledge-related business activities. My research offers a ground work for understanding the paradox - more dispersed high-tech business practices and higher geographic concentration of high-tech jobs in the new economy than before. Drawing from diverse regional and economic literatures, I suggest a paradox of new information communication technology regarding the location pattern of high knowledge-generating jobs. From this perspective, I found a dispersed concentration pattern of high knowledge-generating jobs due to less transitory tacit knowledge than codified knowledge and implicit communication; and business organization change. Both my longitudinal empirical analysis and interviews suggest that the jobs in the high knowledge-generating production industries in the United States became further concentrated during the 1990s.(cont.) During the same period, the jobs in the high knowledge-generating customer-oriented industries dispersed. In the former industries, producers are the major knowledge generators, while in the latter industries, tacit knowledge is derived mostly from the interaction between firms and customers. In consequence, the jobs in the former industries tend to agglomerate with each other, but the jobs in the latter industries tend to disperse in order to be close to customers. Furthermore, five out of the six high-knowledge generating production industries show a "winner-takes-all" kind of spatial monopolization of jobs. For example, in the computer industry, the ratio of the job share of Silicon Valley, the top share holder, and the job share of the Boston metro area, the second highest job share holder, increased from 1.6 in 1990 to 2.9 in 2000. However, this finding fails to explain the phenomenon of R&D units of advanced multinational high-tech production firms locating in remote developing and middle-income countries.(cont.) To answer this puzzle, I identify their actual activities and compare multinational and local R&D operations in Korea. Interviews reveal that they are closer to being customer-relations intensive units, although the R&D units of the multinational firms in Korea are labeled "R&D." They are conduits of outreach to local customers, which conduct (1) the flexible customization of their products to meet local customers' demands and (2) customer management and marketing in the highly competitive global market.by Myounggu Kang.Ph.D

Study of tracking and data acquisition system for the 1990's. Volume 4: TDAS space segment architecture

Tracking and data acquisition system (TDAS) requirements, TDAS architectural goals, enhanced TDAS subsystems, constellation and networking options, TDAS spacecraft options, crosslink implementation, baseline TDAS space segment architecture, and treat model development/security analysis are addressed