Magíster en Ingeniería de Redes de Comunicaciones / Un estudio exhaustivo de las técnicas modernas de modulación es esencial para el diseño de sistemas futuros. Las tecnologías basadas en OFDM, como LTE, se están volviendo más penetrantes a medida que los sistemas descendientes de LTE han adoptado esta técnica de modulación. Los sistemas celulares inalámbricos 5G probablemente seguirán esta tendencia. Es importante estudiar las fortalezas y debilidades de las modulaciones basadas en OFDM para mejorar el rendimiento con las nuevas generaciones. Por esta razón, es esencial determinar qué componentes contribuyen al rendimiento del sistema y eliminar o reemplazar aquellos que no lo hacen. Se estudió un sistema de SC-FDMA usando varios métodos de mapeo de portadoras. En este trabajo se realizó dos tipos de estudios: 1) Análisis exhaustivo del mapeo de las portadoras de SC-FDMA, específicamente SC-LFDMA y SC-IFDMA. Para estudiar las fortalezas y debilidades de SC-LFDMA y SC-IFDMA se genera un escenario donde se considera el canal AWGN y 2) Para poder enfatizar los beneficios de SC-IFDMA se genera dos escenarios: a) Canal con desvanecimiento selectivo en frecuencia y ganancia selectiva de frecuencia usando ruido AWGN y b) Canal con desvanecimiento selectivo en frecuencia usando ruido AWGN. El ruido estudiado en este trabajo es el AWGN. Específicamente se quiere estudiar el beneficio d e los tipos de mapeo de portadoras usando redundancia. Como escenario de control se utiliza el mismo esquema pero sin redundancia. La modulación ascendente de LTE implementa SC-LFDMA, que tiene un PAPR alto comparado con el SC-IFDMA. Se argumenta que SC-LFDMA tiene un alto Eb/N0, sin embargo, aquí se demuestra que sólo la varianza de la Eb/N0 se incrementa, pero el promedio sigue siendo el mismo en un escenario donde se considera el canal AWGN. En un canal con desvanecimiento selectivo en frecuencia usando ruido AWGN, la Eb/N0 de SC-IFDMA es superior a SC-LFDMA, en el escenario de control y también para el caso con redundancia. Para un canal con desvanecimiento selectivo en frecuencia y ganancia selectiva de frecuencia usando ruido AWGN se demuestra que la Eb/N0 de SC-LFDMA es superior a SC-IFDMA en un escenario con redundancia, pero al tener alto BER el SC-LFDMA, el SC-IFDMA es mejor. Para el escenario de control, la Eb/N0 de SC-IFDMA es igual a SC-LFDMA, pero al tener alto BER el SC-LFDMA, el SC-IFDMA es mejor. En términos de PAPR, para todos los casos y escenarios el SC-IFDMA tiene un PAPR bajo comparado con el SC-LFDMA. A pesar de que LTE utiliza SC-LFDMA, las tecnologías futuras deberían considerar el estudio de los beneficios del SC-IFDMA, ya que se demuestra que tiene mucho que ofrecer. En particular, para las transmisiones ascendentes, ya que es más eficiente desde el punto de vista energético y no parece haber un compromiso de rendimiento significativo. Por lo tanto, se debe seleccionar una técnica de modulación de PAPR baja, tal como SC-IFDMA, para transmisiones ascendentes de redes celulares inalámbricas de próxima generación.

Currently there is a need to design, develop, and deploy autonomous and portable indoor geolocation systems to fulfil the needs of military, civilian, governmental and commercial customers where GPS and GLONASS signals are not available due to the limitations of both GPS and GLONASS signal structure designs. The goal of this dissertation is (1) to introduce geolocation systems; (2) to classify the state of the art geolocation systems; (3) to identify the issues with the state of the art indoor geolocation systems; and (4) to propose and assess four WPI indoor geolocation systems. It is assessed that the current GPS and GLONASS signal structures are inadequate to overcome two main design concerns; namely, (1) the near-far effect and (2) the multipath effect. We propose four WPI indoor geolocation systems as an alternative solution to near-far and multipath effects. The WPI indoor geolocation systems are (1) a DSSS/CDMA indoor geolocation system, (2) a DSSS/CDMA/FDMA indoor geolocation system, (3) a DSSS/OFDM/CDMA/FDMA indoor geolocation system, and (4) an OFDM/FDMA indoor geolocation system. Each system is researched, discussed, and analyzed based on its principle of operation, its transmitter, the indoor channel, and its receiver design and issues associated with obtaining an observable to achieve indoor navigation. Our assessment of these systems concludes the following. First, a DSSS/CDMA indoor geolocation system is inadequate to neither overcome the near-far effect not mitigate cross-channel interference due to the multipath. Second, a DSSS/CDMA/FDMA indoor geolocation system is a potential candidate for indoor positioning, with data rate up to 3.2 KBPS, pseudorange error, less than to 2 m and phase error less than 5 mm. Third, a DSSS/OFDM/CDMA/FDMA indoor geolocation system is a potential candidate to achieve similar or better navigation accuracy than a DSSS/CDMA indoor geolocation system and data rate up to 5 MBPS. Fourth, an OFDM/FDMA indoor geolocation system is another potential candidate with a totally different signal structure than the pervious three WPI indoor geolocation systems, but with similar pseudorange error performance.

Abstract The demand in mobile broadband communications is increasing dramatically. It is expected that 1000 times more mobile-network capacity will be needed within 10 years. Multiple-input, multiple-output (MIMO) antenna configuration and spatial multiplexing are among the essential techniques for reaching the targets. This creates motivation for study of advanced receivers for combating inter-antenna interference (IAI) and inter-symbol interference (ISI). While various receiver structures have been extensively considered for MIMO receivers, the emphasis has been on those operating in downlink orthogonal frequency-division multiple access (OFDM) systems, wherein ISI is not a problem. Advanced receiver structures for single-carrier frequency-division multiple access (SC-FDMA) uplink systems were studied and analysed. Various receivers were compared via MATLAB simulations, with the objective being to gain solid understanding of how they perform in different channel environments. An efficient combination of IAI and ISI equalisation for SC-FDMA receivers is proposed. The proposed receiver architecture is shown to be a considerable improvement over the conventional linear minimum mean-square error (LMMSE) receiver. Several MIMO detector algorithms and their performance–complexity characteristics are presented. The K-best algorithm with a list size of 8 is shown to be the best option for practical MIMO detector implementation of this receiver in the 4x4 MIMO 64-level quadrature amplitude modulation (QAM) scenario. The second objective involved examining the implementation aspects of the 8-best receiver to achieve good understanding of the complexity of various implementation architectures. It emerged that avoiding the sorting operation in the 8-best list sphere detector (LSD) tree-search algorithm implementation is not recommendable in the 4x4 MIMO 64-QAM scenario. Several field-programmable gate array (FPGA) implementations were carried out, with a range of high-level synthesis (HLS) tools. It is shown that HLS tools have improved significantly and are especially favourable for prototyping of large designs. Additionally, the importance of FPGA technology selection is addressed. Smaller silicon technology should be exploited if base-station baseband processing power consumption is to be minimised. The potential performance or complexity-related gain with the latest FPGAs should be taken into account in comparison of the performance–complexity characteristics of the algorithms. Differences of a few tens of per cent in estimated complexity or performance between two algorithms are often below the threshold of what can be gained or lost in the practical implementation process. / Tiivistelmä Tiheään asuttujen kaupunkien uudet langattomat palvelut tarvitsevat tietoliikenneverkkoja, jotka mahdollistavat suuremman tiedonsiirtonopeuden ja kapasiteetin kuin sen, jonka nykyiset mobiiliverkot voivat tarjota. On arveltu, että mobiiliverkkojen kapasiteetin tarve tuhatkertaistuu seuraavan kymmenen vuoden aikana. Tuhatkertainen kapasiteetti on arvioitu saavutettavan kasvattamalla kolmea eri osa-aluetta kymmenkertaiseksi: taajuusspektrin määrä, spektrin käytön tehokkuus sekä tukiasematiheys. Tämä väitöskirja keskittyy spektrin käytön tehokkuuden kasvattamiseen. Moniantennitoteutus (multiple-input multiple-output, MIMO) on siinä välttämätön. MIMO-tekniikkaa hyödyntävien solukkojärjestelmien tukiasemavastaanottimissa tarvitaan melko monimutkainen kanavakorjain sekä ilmaisin, joiden algoritmien optimointi ja toteutus ymmärretään vielä sangen puutteellisesti. Väitöskirjatutkimuksen päätavoitteena on tutkia edistyksellisiä vastaanotinrakenteita, joilla saavutetaan LTE-A-standardin tavoitetiedonsiirtonopeus kohtuullisella kompleksisuudella. Työssä keskitytään ns. nousevaan siirtosuuntaan (uplink) eli päätelaitteesta tukiasemaan tapahtuvaan tiedonsiirtoon, jossa käytetään yhden kantoaallon taajuusjakomonikäyttötekniikkaa (single-carrier frequency-division multiple-access, SC-FDMA) ortognaalisen taajuusjakomonikäytön (orthogonal frequency division multiple access, OFDMA) sijaan. Eri vastaanotinrakenteita ja näiden ilmaisinalgoritmeja vertaillaan tietokonesimuloinnein MATLAB-ympäristössä. Väitöskirjassa ehdotetaan kaksiosaista vastaanotinrakennetta, jossa antennien välinen keskinäishäiriö (inter antenna interference, IAI) ja symbolien välinen keskinäisvaikutus (intersymbol interference, ISI) poistetaan kahdessa eri vaiheessa. Tietokoneimulaatiot osoittavat ko. rakenteen parantavan suorituskykyä huomattavasti perinteiseen lineaariseen keskineliövirheen minimoivaan (linear minimum mean square error, LMMSE) vastaanottimeen verrattuna. Nk. K parasta polkua valitsevan MIMO-ilmaisinalgoritmin listan koolla kahdeksan todetaan tarjoavan 4x4 MIMO 64-tasoisen kvadratuuriamplitudimodulaation (quadrature amplitude modulation, QAM) ympäristössä parhaan kompromissin suorituskyvyn ja kompleksisuuden suhteen. Käytännön toteutettavuuden kannalta keskitytään ohjelmoitavaan digitaalipiiritoteutukseen (field-programmable gate array, FGPA) ja ns. korkean tason synteesi (high-level synthesis, HLS) -työkalujen käyttöön vastaanottimen suunnittelussa. K parasta polkua valitsevan MIMO-ilmaisinalgoritmin arkkitehtuurivertailut osoittavat, että sinänsä vaativaa lajittelualgoritmia ei aina kannata yrittää välttää kirjallisuudessa aikaisemmin ehdotetulla ratkaisulla. Useita eri HLS työkaluja käytetään FPGA toteutuksissa ja todetaan että työkalut ovat kehittyneet huomattavasti viimeisen kahdeksan vuoden aikana. Lisäksi todetaan, että 16 nm viivanleveyden piireillä voidaan saavuttaa noin 15 % suurempi ilmaisunopeus ja 60 % pienempi tehonkulutus verrattuna 28 nm viivanleveyttä käyttäviin piireihin. Erityisesti potentiaali tehonkulutuksen minimoiseksi kannattaa hyödyntää, mikäli signaalinkäsittely näyttelee merkittävää roolia vastaanottimen kokonaistehonkulutuksessa. Kokonaisuutena todetaan, että toteutukseen liittyvät valinnat sekä vaikutus lopputulokseen, tulisi ottaa huomioon jo algoritmien valinnassa. Pieni ero kahden eri algoritmin suorituskyvyn välillä häviää helposti toteutusvaiheen ratkaisujen vaikutusten alle.

<p>3GPP LTE (Long Term Evolution) is a project of the Third Generation Partnership Project to improve the UMTS (Universal Mobile Telecommunications System) mobile phone standard to cope with future technology evolutions. Two duplex schemes FDD and TDD are investigated in this thesis. Several computational intensive components of the baseband processing for LTE uplink such as synchronization, channel estimation, equalization, soft demapping, turbo decoding is analyzed. Cost analysis is hardware independent so that only computational complexity is considered in this thesis. Hardware dependent discussion for LTE baseband SDR platform is given according the analysis results.</p>

<p>One goal in the development of future cellular systems is to increase performance. Channel dependent scheduling can possibly contribute to a performance enhancement. It requires channel qualityinformation and uplink channel knowledge is often incomplete. This master thesis work compares channel dependent scheduling and channel independent scheduling for a Single Carrier Frequency Division Multiple Access-based uplink in time domain and time and frequencydomain assuming continuous channel quality information updates. It also evaluates different methods for providing channel quality information by investigating how the limited channel knowledge they supply affects the performance of channel dependent scheduling.</p><p>Single-cell simulations with perfect channel knowledge indicate small gains for channel dependent scheduling. Large gains are seen when performing frequency and time domain scheduling instead of only time domain scheduling. Limited channel knowledge causes performance loss for channel dependent scheduling. The performance is only slightly decreased if a method with sufficiently frequent providing of channel quality information updates is applied.</p><p>More realistic multi-cell simulations show large gains for channel dependent scheduling. It is possible that these results are influenced by link adaptation and scheduling problems due to non predictable interference when performing dynamic scheduling. In the comparison between channel dependent and channel independent scheduling the channel dependent scheduling can benefit from the fact that the selected channel dependent scheduling algorithms result in a more static scheduling than the selected channel independent scheduling algorithms do.</p>

One goal in the development of future cellular systems is to increase performance. Channel dependent scheduling can possibly contribute to a performance enhancement. It requires channel qualityinformation and uplink channel knowledge is often incomplete. This master thesis work compares channel dependent scheduling and channel independent scheduling for a Single Carrier Frequency Division Multiple Access-based uplink in time domain and time and frequencydomain assuming continuous channel quality information updates. It also evaluates different methods for providing channel quality information by investigating how the limited channel knowledge they supply affects the performance of channel dependent scheduling. Single-cell simulations with perfect channel knowledge indicate small gains for channel dependent scheduling. Large gains are seen when performing frequency and time domain scheduling instead of only time domain scheduling. Limited channel knowledge causes performance loss for channel dependent scheduling. The performance is only slightly decreased if a method with sufficiently frequent providing of channel quality information updates is applied. More realistic multi-cell simulations show large gains for channel dependent scheduling. It is possible that these results are influenced by link adaptation and scheduling problems due to non predictable interference when performing dynamic scheduling. In the comparison between channel dependent and channel independent scheduling the channel dependent scheduling can benefit from the fact that the selected channel dependent scheduling algorithms result in a more static scheduling than the selected channel independent scheduling algorithms do.

ITC/USA 2012 Conference Proceedings / The Forty-Eighth Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2012 / Town and Country Resort & Convention Center, San Diego, California / We propose a spectrally-efficient multiple-access technique that is particularly suitable for aeronautical telemetry applications involving serial streaming of data from multiple test articles to a ground station. Unlike conventional frequency-division multiple access, we assign overlapping frequency bands to different users with a minimum carrier separation corresponding to the symbol rate. We utilize multiuser detection strategies at the ground station to separate the transmissions from different test articles. As shown by the simulation results, the proposed scheme is robust to large frequency offsets due to oscillator offsets and Doppler shifts commonly encounters in aeronautical telemetry applications.

Techn. Universiẗat, Diss., 2004--Darmstadt.

Τα τελευταία χρόνια παρατηρείται μια ραγδαία ανάπτυξη στο κλάδο των τηλεπικοινωνιών και αυτό είναι ορατό στην καθημερινή ζωή μας. Η ψηφιακή μετάδοση και επεξεργασία των σημάτων σε συνδυασμό με την βελτίωση των μέσων μετάδοσης, της υποδομής και των τεχνικών διαμόρφωσης, δίνουν την δυνατότητα στους επιστήμονες να επικεντρωθούν όλο και περισσότερο στα θέματα τηλεπικοινωνιών, ειδικά των ασύρματων τηλεπικοινωνιών. Στις ασύρματες τηλεπικοινωνίες οι τεχνικές πολλαπλής πρόσβασης χρησιμοποιούνται για να επιτρέψουν σε πολλούς χρήστες να μοιραστούν ταυτόχρονα ένα περιορισμένο φάσμα συχνοτήτων. Το μοίρασμα του φάσματος είναι απαραίτητο προκειμένου να αυξήσουμε την χωρητικότητα ενός συστήματος, ενώ θα πρέπει να γίνει με τέτοιο τρόπο, ώστε να μην υπάρχει σημαντική υποβάθμιση της απόδοσης του συστήματος. Για να αντιμετωπιστεί αυτή η υποβάθμιση έχουν προταθεί διάφορες τεχνικές πολλαπλής πρόσβασης. Σε μια από αυτές τις τεχνικές το συνολικό φάσμα συχνοτήτων διαιρείται σε συχνοτικά μη-επικαλυπτόμενες υποζώνες, οι οποίες ανατίθενται στους επιμέρους χρήστες (πολλαπλή πρόσβαση με διαίρεση συχνότητας – FDMA). Σε αυτή την περίπτωση, όμως, έχουμε σπατάλη του εύρους ζώνης του καναλιού, αφού οι χρήστες δεν μπορούν να χρησιμοποιούν όλο το κανάλι, όλη την ώρα. Μια τεχνική που δίνει λύση στο παραπάνω πρόβλημα (πολλαπλή πρόσβαση με διαίρεση κωδικών - CDMA), χρησιμοποιεί ορθογώνιους κώδικες που ανατίθενται στους χρήστες, δίνοντας τους την δυνατότητα ταυτόχρονης μετάδοσης στο κανάλι για όση ώρα απαιτείται. Το βασικότερο πρόβλημα αυτής της τεχνικής είναι ότι η ιδιότητα της ορθογωνιότητας των κωδίκων χάνεται όταν χρησιμοποιούνται συχνοτικά επιλεκτικά κανάλια. Μια νέα τεχνική πολλαπλής πρόσβασης που προτάθηκε η οποία αποφεύγει τα παραπάνω προβλήματα είναι η πολλαπλή πρόσβαση με διαίρεση συχνότητας και αναδιάταξη δεδομένων (Interleaved FDMA). Η συγκεκριμένη τεχνική συνδυάζει χαρακτηριστικά από το FDMA και το CDMA. Συγκεκριμένα, συμπιέζει χρονικά την ακολουθία συμβόλων που πρόκειται να αποσταλεί, την επαναλαμβάνει (παρόμοια λειτουργία με το CDMA) και την μετατοπίζει συχνοτικά βασιζόμενη στον εκάστοτε χρήστη (παρόμοια λειτουργία με το OFDMA). Στον δέκτη οι ακολουθίες των χρηστών διαχωρίζονται χωρίς πρόβλημα ακόμα και όταν το κανάλι είναι συχνοτικά επιλεκτικό. Σε αυτή την περίπτωση εισάγεται διασυμβολική παρεμβολή με αποτέλεσμα να απαιτείται κάποια διαδικασία ισοστάθμισης. Η δομή με βάση την οποία έγινε η μελέτη της τεχνικής πολλαπλής πρόσβασης IFDMA είναι η εξής: 1. Αναφορά στις τρέχουσες τεχνικές πολλαπλής πρόσβασης και στα πλεονεκτήματα και τα μειονεκτήματα της κάθε τεχνικής. 2. Μελέτη της τεχνικής IFDMA και αναφορά στα προβλήματα που εμφανίζει πχ ισοστάθμιση. 3. Παρουσίαση της υλοποίησης της τεχνικής IFDMA και των λύσεων για τα προβλήματα που παρουσιάζει, τα πειραματικά αποτελέσματα που σχετίζονται με την υλοποίηση, καθώς και συγκριτικά αποτελέσματα με τις πιο γνωστές τεχνικές πολλαπλής πρόσβασης. 4. Συμπεράσματα της μελέτης και της σύγκρισης της τεχνικής IFDMA με τις γνωστές τεχνικές πολλαπλής πρόσβασης, καθώς και πιθανές μελλοντικές κατευθύνσεις. / In recent years, we have seen a rapid growth in the telecom industry and this is evident in our everyday lives. The digital transmission and processing of signals in conjunction with the improvement of the transmission, infrastructure and technical configuration means, gives scientists the opportunity to focus increasingly on telecommunications issues, specifically on wireless telecommunications. In wireless telecommunications, multiple access techniques are used, in order to allow multiple users to share simultaneously a limited range of frequencies. Spectrum splitting is necessary, in order to increase the capacity of a system and should be done in a way that results in no significant degradation of system performance. To overcome this degradation various multiple access techniques have been proposed. According to one of these techniques, the total frequency spectrum is divided in frequency of non-overlapping sub-bands which are assigned to individual users (multiple access frequency division - FDMA). In this case, however, we are wasting the bandwidth of the channel, since users can not use all the channel, all the time. A technique that solves the above problem (multiple access with codes - CDMA) uses orthogonal codes, assigned to users, allowing them to simulcast in the channel for as long as needed. The main problem of this technique is that the status of orthogonality is lost when frequency selective channels are used. A new multiple access technique proposed, which avoids these problems, is the multiple access with frequency division and reorganization of data (Interleaved FDMA). This technique combines features from FDMA and CDMA. Specifically, it compresses timewise the sequence of symbols to be sent, repeats it (an operation similar to CDMA) and shifts it, in terms of frequency range, based on each user (a function similar to OFDMA). In the receptor’s side, the sequences of users separate without problem, even when the channel is frequency selective. In this case, intersymbol interference is introduced, which, therefore, requires an equalization process. The structure, upon which the study of the multiple access technique IFDMA made, was: 1. Reference to the current multiple-access techniques and the advantages and disadvantages of each one of them. 2. Study of the IFDMA technique and reference to the problems that it presents e.g. equalization. 3. Presentation of the implementation of a) the IFDMA technique, b) solutions for the problems it displays, c) experimental results and d) the results from the comparison against the most popular multiple-access techniques. 4. Conclusions, stemming from the study and the comparison of the IFDMA technique with the known multiple-access techniques; possible future prospects.

3GPP LTE (Long Term Evolution) is a project of the Third Generation Partnership Project to improve the UMTS (Universal Mobile Telecommunications System) mobile phone standard to cope with future technology evolutions. Two duplex schemes FDD and TDD are investigated in this thesis. Several computational intensive components of the baseband processing for LTE uplink such as synchronization, channel estimation, equalization, soft demapping, turbo decoding is analyzed. Cost analysis is hardware independent so that only computational complexity is considered in this thesis. Hardware dependent discussion for LTE baseband SDR platform is given according the analysis results.