In the last decade, there has been an explosive growth in different applications of wireless technology, due to users' increasing expectations for multi-media services. With the current trend, the present systems will not be able to handle the required data traffic. Lattice codes have attracted considerable attention in recent years, because they provide high data rate constellations. In this thesis, the applications of implementing lattice codes in different communication systems are investigated. The thesis is divided into two major parts. Focus of the first part is on constellation shaping and the problem of lattice labeling. The second part is devoted to the lattice decoding problem. In constellation shaping technique, conventional constellations are replaced by lattice codes that satisfy some geometrical properties. However, a simple algorithm, called lattice labeling, is required to map the input data to the lattice code points. In the first part of this thesis, the application of lattice codes for constellation shaping in Orthogonal Frequency Division Multiplexing (OFDM) and Multi-Input Multi-Output (MIMO) broadcast systems are considered. In an OFDM system a lattice code with low Peak to Average Power Ratio (PAPR) is desired. Here, a new lattice code with considerable PAPR reduction for OFDM systems is proposed. Due to the recursive structure of this lattice code, a simple lattice labeling method based on Smith normal decomposition of an integer matrix is obtained. A selective mapping method in conjunction with the proposed lattice code is also presented to further reduce the PAPR. MIMO broadcast systems are also considered in the thesis. In a multiple antenna broadcast system, the lattice labeling algorithm should be such that different users can decode their data independently. Moreover, the implemented lattice code should result in a low average transmit energy. Here, a selective mapping technique provides such a lattice code. Lattice decoding is the focus of the second part of the thesis, which concerns the operation of finding the closest point of the lattice code to any point in N-dimensional real space. In digital communication applications, this problem is known as the integer least-square problem, which can be seen in many areas, e.g. the detection of symbols transmitted over the multiple antenna wireless channel, the multiuser detection problem in Code Division Multiple Access (CDMA) systems, and the simultaneous detection of multiple users in a Digital Subscriber Line (DSL) system affected by crosstalk. Here, an efficient lattice decoding algorithm based on using Semi-Definite Programming (SDP) is introduced. The proposed algorithm is capable of handling any form of lattice constellation for an arbitrary labeling of points. In the proposed methods, the distance minimization problem is expressed in terms of a binary quadratic minimization problem, which is solved by introducing several matrix and vector lifting SDP relaxation models. The new SDP models provide a wealth of trade-off between the complexity and the performance of the decoding problem.

In the last decade, there has been an explosive growth in different applications of wireless technology, due to users' increasing expectations for multi-media services. With the current trend, the present systems will not be able to handle the required data traffic. Lattice codes have attracted considerable attention in recent years, because they provide high data rate constellations. In this thesis, the applications of implementing lattice codes in different communication systems are investigated. The thesis is divided into two major parts. Focus of the first part is on constellation shaping and the problem of lattice labeling. The second part is devoted to the lattice decoding problem. In constellation shaping technique, conventional constellations are replaced by lattice codes that satisfy some geometrical properties. However, a simple algorithm, called lattice labeling, is required to map the input data to the lattice code points. In the first part of this thesis, the application of lattice codes for constellation shaping in Orthogonal Frequency Division Multiplexing (OFDM) and Multi-Input Multi-Output (MIMO) broadcast systems are considered. In an OFDM system a lattice code with low Peak to Average Power Ratio (PAPR) is desired. Here, a new lattice code with considerable PAPR reduction for OFDM systems is proposed. Due to the recursive structure of this lattice code, a simple lattice labeling method based on Smith normal decomposition of an integer matrix is obtained. A selective mapping method in conjunction with the proposed lattice code is also presented to further reduce the PAPR. MIMO broadcast systems are also considered in the thesis. In a multiple antenna broadcast system, the lattice labeling algorithm should be such that different users can decode their data independently. Moreover, the implemented lattice code should result in a low average transmit energy. Here, a selective mapping technique provides such a lattice code. Lattice decoding is the focus of the second part of the thesis, which concerns the operation of finding the closest point of the lattice code to any point in N-dimensional real space. In digital communication applications, this problem is known as the integer least-square problem, which can be seen in many areas, e.g. the detection of symbols transmitted over the multiple antenna wireless channel, the multiuser detection problem in Code Division Multiple Access (CDMA) systems, and the simultaneous detection of multiple users in a Digital Subscriber Line (DSL) system affected by crosstalk. Here, an efficient lattice decoding algorithm based on using Semi-Definite Programming (SDP) is introduced. The proposed algorithm is capable of handling any form of lattice constellation for an arbitrary labeling of points. In the proposed methods, the distance minimization problem is expressed in terms of a binary quadratic minimization problem, which is solved by introducing several matrix and vector lifting SDP relaxation models. The new SDP models provide a wealth of trade-off between the complexity and the performance of the decoding problem.

In todays society, a growing number of users are demanding more sophisticated services from wireless communication devices. In order to meet these rising demands, it has been proposed to increase the capacity of the wireless channel by using more than one antenna at the transmitter and receiver, thereby creating multiple-input multiple-output (MIMO) channels. Using MIMO communication techniques is a promising way to improve wireless communication technology because in a rich-scattering environment the capacity increases linearly with the number of antennas. However, increasing the number of transmit antennas also increases the complexity of detection at an exponential rate. So while MIMO channels have the potential to greatly increase the capacity of wireless communication systems, they also force a greater computational burden on the receiver. Even suboptimal MIMO detectors that have relatively low complexity, have been shown to achieve unprecedented high spectral efficiency. However, their performance is far inferior to the optimal MIMO detector, meaning they require more transmit power. The fact that the optimal MIMO detector is an impractical solution due to its prohibitive complexity, leaves a performance gap between detectors that require reasonable complexity and the optimal detector. The objective of this research is to bridge this gap and provide new solutions for managing the inherent performance-complexity trade-off in MIMO detection. The optimally-ordered decision-feedback (BODF) detector is a standard low-complexity detector. The contributions of this thesis can be regarded as ways to either improve its performance or reduce its complexity - or both. We propose a novel algorithm to implement the BODF detector based on noise-prediction. This algorithm is more computationally efficient than previously reported implementations of the BODF detector. Another benefit of this algorithm is that it can be used to easily upgrade an existing linear detector into a BODF detector. We propose the partial decision-feedback detector as a strategy to achieve nearly the same performance as the BODF detector, while requiring nearly the same complexity as the linear detector. We propose the family of Chase detectors that allow the receiver to trade performance for reduced complexity. By adapting some simple parameters, a Chase detector may achieve near-ML performance or have near-minimal complexity. We also propose two new detection strategies that belong to the family of Chase detectors called the B-Chase and S-Chase detectors. Both of these detectors can achieve near-optimal performance with less complexity than existing detectors. Finally, we propose the double-sorted lattice-reduction algorithm that achieves near-optimal performance with near-BODF complexity when combined with the decision-feedback detector.

Emerging "bandwidth hungry" applications such as high definition video distribution and ultra fast multimedia side-loading have extended the need for multi-gigabit wireless solutions beyond the reach of conventional WLAN technology or even more recently emerging UWB and MIMO systems. The availability of 7GHz of unlicensed bandwidth in the 60GHz spectrum, represents a unique opportunity to address such data-throughput requirements. The 60GHz Integrated CMOS digital radio chipset comprises of PHY and MAC layers, RF transceiver, High-Speed Digital Interface and an underlying Serial Communication Fabric. To have a complete communication solution compliant with the latest ECMA-369, ISO/DIS 13156 and IEEE 802.15.3c standards, we build a million gate digital implementation of MAC and PHY. The Serial Peripheral Interface (SPI) serves as the bridge between the higher layers in the communication stack (PAL-MAC) and the lower layers like PHY-RF Front End. The MAC module can setup the communication link on the fly by tuning parameters such as operating channel, channel bonding and bandwidth, data rates, error correction mechanisms, handshaking mechanisms, etc, by using the SPI to communicate with internal components. The SPI interface plays a crucial rule in not only this, but also during the testing and debug phase. Operation of each of the RF modules is monitored through the serial interface using local SPI slaves which are hooked up to the 4-wire serial bus running all through the chip. The SPI host controller emulates an embedded protocol analyzer. For calibration and fine tuning purposes, digital settings can also be loaded onto these modules through the SPI interface. R-2R DACs are used to convert these commands into analog voltages which then provide a tunable bias to the RF and mixed-signal modules. Other key functions of this serial communication and control interface are: Initialization of all of the RF and mixed signal modules, DC calibration of data converter, PLL and other mixed-signal modules, data acquisition, parametric tuning for digital modules such as linear equalizer, Gain Control loops (AGC, VGA), etc. Ultra high speed digital Input-Output buffers are used to provide an external data interface to the radio chipset. These high speed I/Os are also used in the gbps (gigabit-per-second) link for data transfer between the RF transceiver chip and the PHY-MAC baseband chip. The IOs are expected to comply with different signaling standards such as LVDS, SLVS200, SLVS400, etc. A robust system involves a meticulous pad ring design with proper power domains and power cuts. Full-chip integration of the digital PHY, MAC, peripheral logic and IO ring is done in a semi-custom fashion.

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M. Tech. Electrical Engineering. / Discusses MIMO systems have been hailed for the benefits of enhancing the reliability of the wireless communication link and increasing of the channel capacity, however the complexity of MIMO encoding and decoding algorithms increases considerably with the number of antennas. This research aims to suggest an optimisation approach to a reduced complexity implementation of the Alamouti 4×2 STBC. This is achieved by considering the FPGA parallelisation of the conditionally optimised ML decoding algorithm. The above problem can be divided into two subproblems. 1. The ML decoding of the Double Alamouti 4×2 STBC has a high computational cost when an exhaustive search is performed on the signal constellation for M-ary QAM. 2. Though the conditionally optimised ML decoding leads to less computational complexity compared to the full generic ML detection algorithm, the practical implementation remains unattractive for wireless systems.

Τα τελευταία χρόνια και κυρίως μετά το 1996 έχει παρουσιαστεί ένα έντονο ενδιαφέρον γύρω από τα ασύρματα συστήματα MIMO (Συστήματα Πολλών Εισόδων και Πολλών Εξόδων). Η βασική αιτία που δημιούργησε αυτό το ενδιαφέρον ήταν η θεωρητική ανάλυση της χωρητικότητας που επιτυγχάνεται με τη χρήση πολλαπλών κεραιών τόσο στο δέκτη όσο και στον πομπό. Ωστόσο πέρα από την αύξηση της χωρητικότητας τα συστήματα MIMΟ έχουν μια σειρά από επιπλέον πλεονεκτήματα, επιτυγχάνουν ανεκτικότητα στην εξασθένιση, αυξάνουν την φασματική αποδοτικότητα, μειώνουν την κατανάλωση ενέργειας καθώς και το κόστος χρήσης και κατασκευής ασύρματων δικτύων. Έχοντας λάβει υπ’ όψιν τα παραπάνω και έχοντας κάνει ήδη μια αρχική έρευνα στο τι υπάρχει στην επιστημονική βιβλιογραφία γύρω από τα συστήματα MIMO, επιλέξαμε να ασχοληθούμε με την συγκεκριμένη τεχνολογία και πιο συγκεκριμένα με την προ-κωδικοποίηση πομπού, όταν τα κανάλια που διαθέτουμε είναι συχνοτικά επιλεκτικά (frequency selective). Το πρόβλημα που μας απασχόλησε είναι η διερεύνηση τεχνικών κωδικοποίησης των δεδομένων του πομπού, πριν αυτά μεταδοθούν, ούτως ώστε να μπορέσει να απλοποιηθεί η σχεδίαση του δέκτη. Στην περίπτωση των συχνοτικά επιλεκτικών καναλιών πέρα από τον πανταχού παρόντα Γκαουσιανό θόρυβο έχουμε να αντιμετωπίσουμε και τη διασυμβολική παρεμβολή (Intersymbol Interference - ISI) . Στόχος μας είναι να μπορέσουμε να μετατοπίσουμε τη διαδικασία της ισοστάθμισης από το δέκτη στον πομπό, όπου, στην περίπτωση που ο πομπός είναι ένας σταθμός βάσης, η δυνατότητα υλοποίησης πολύπλοκων διεργασιών είναι μεγαλύτερη, τόσο μεγαλύτερης ανοχής στην κατανάλωση ενέργειας όσο κυρίως, και στη δυνατότητα χρήσης πολύπλοκου υλικού. Το πρόβλημα που τίθεται στην περίπτωση που η ισοστάθμιση γίνει στην μεριά του πομπού είναι η ποιότητα και η ποσότητα της γνώσης του πραγματικού καναλιού. Είναι σχεδόν αδύνατο ο πομπός να έχει πλήρη γνώση του πραγματικού καναλιού, με αποτέλεσμα να πρέπει να αρκεστεί σε γνώση, που στην καλύτερη περίπτωση προσεγγίζει αυτή του πραγματικού καναλιού. Επίσης, πολλές φορές, η ποσότητα της γνώσης που μπορεί να αποσταλεί από το δέκτη – όταν δεν ισχύει η αρχή της αμοιβαιότητας (reciprocity) – είναι περιορισμένη. Από τα παραπάνω καταλαβαίνουμε ότι θα είχε ενδιαφέρον η μελέτη τεχνικών που παρουσιάζουν ανοχή στην ποιότητα της γνώσης του καναλιού καθώς και η συμπεριφορά τους όταν αυτές διαθέτουν μερική ή και περιορισμένη γνώση του πραγματικού καναλιού. Ένας από τους τρόπου αντιμετώπισης όταν συναντούνται συχνοτικά επιλεκτικά κανάλια είναι η χρήση του OFDM με όσα αρνητικά αυτό συνεπάγεται (π.χ. η δυσκολία συγχρονισμού πομπού και δέκτη). Ένας άλλος τρόπος αντιμετώπισης, στην περίπτωση μονής φέρουσας (single carrier), είναι η χρήση προκωδικοποιητων Bezout. Επιλέξαμε να ασχοληθούμε με αυτόν τον τύπου προκωδικοποίητων. Πιο συγκεκριμένα, όταν ο αριθμός των κεραιών του πομπού είναι μεγαλύτερος από τον αριθμό των κεραιών του δέκτη, είναι δυνατόν να εφαρμόσουμε την ταυτότητα Bezout (Bezout Identity) στην μεριά του δέκτη. Με απλά λόγια θα εφαρμόσουμε ένα προ-ισοσταθμιστή επιβολής μηδενικών (zero forcing). Όπως είναι αναμενόμενο, μιας και ο προκωδικοποιητής εφαρμόζεται στην μεριά του πομπού, πριν εμφανιστεί ο Γκαουσιανός θόρυβος, δεν έχουμε ενίσχυση αυτού του θορύβου, ωστόσο είναι δυνατόν να έχουμε σημαντική αύξηση της μεταδιδόμενης ισχύος. Για να λυθεί αυτό το πρόβλημα έχει προταθεί στη βιβλιογραφία η σχεδίαση προκωδικοποιητών Bezout με την χρήση περιορισμών ισχύος. Αυτό που εμείς μελετήσαμε στην περίπτωση των προκωδικοποιητών Bezout (ή FIR προκωδικοποιητών), είναι η συμπεριφορά τους στην περίπτωση που ο πομπός διαθέτει πλήρη ή μερική γνώση του καναλιού. Είδαμε την περίπτωση του σχεδιασμού ενός FIR προκωδικοποιητή κάτω από τον περιορισμό ισχύος μετάδοσης μέσω της μεθόδου Tikhonov Regularization, ενός σημαντικού εργαλείου επίλυσης του προβλήματος των ελαχίστων τετραγώνων κάτω από τη δι-κριτήριο διατύπωση. Τέλος, προτείναμε δύο FIR σχεδιασμούς προκωδικοποιητών για την περίπτωση που ο πομπός διαθέτει παραμετρική (στατιστική) περιγραφή του καναλιού. / The last years, but mainly after 1996 there is an intensive interest in MIMO systems. The reason that created this interest was the capacity that can be achieved by the use of multiple antennas to the transmitter and to receiver. Furthermore, the use of multiple antennas has a number of advantages except from the capacity increase; MIMO can achieve tolerance to fading, spectral efficiency, increased coverage etc. By having considered the above information we decided to work with MIMO systems and especially with precoding techniques for frequency selective channels. In the case of frequency selective channels except from the Gaussian noise we have to treat and with intersymbol interference (ISI) which is an important degradation factor. A very serious reason to handle intersymbol interference at the transmitter side - especially when transmitter is a base station - is to simplify receiver's design. When transmitter is a base station there is a tolerance in power consuming and in the implementation of more complicated hardware. After an extensive bibliographical we concluded to use the theory of Bezout Identity. In the case where the number of antennas at the transmitter is greater than the number of antennas at the receiver it is formed a left-coprime FIR channel. By using the Bezout identity matrix, it is possible to be designed a FIR MIMO precoder that reduce intersymbol interference. Bezout precoder (pre-equalizer) is a zero-forcing (ZF) equalizer. As it is known from bibliography ZF equalizer has the disadvantage that amplifies noise power in deep fades. For the case of Bezout precoder it is not true since there is no noise - noise will appear at the receiver. But there is another disadvantage, Bezout precoder may increase transmit power significantly to overcome deep fades in the singular values of the channel matrix. The solution to the previous phenomenon can be taken by designing ZF precoders under power constraints. The main problem in the case of transmit precoding is the channel knowledge - when reciprocity principle is not valid. In most cases it is not possible to have perfect channel knowledge or even the knowledge that we have may be of bad quality. Another drawback that appears in the case of frequency selective channels is the amounts of information (number of bits) that can be send back to the transmitter - limited feedback. Many works assumed a quasi-static channel - channel doesn't changes for a number of symbols - and perfect channel knowledge. In real world this may not be true. In this master thesis we investigated three things. Firstly, the behavior of Bezout precoders under channel mismatch at the side of transmitter. Secondly, ways that will allows us to decrease channel feedback. And thirdly, which was the most interesting, we proposed two FIR designs that uses statistical channel knowledge.

Concurrent cooperative transmission (CCT) occurs when a collection of power-constrained single-antenna radios transmit simultaneously to form a distributed multi-input and multi-output (DMIMO) link. DMIMO can be a means for highly reliable and low-latency cooperative routing, when the MIMO channel is exploited for transmit and receive diversity; in this context, the range extension benefit is emphasized. Alternatively, DMIMO can be a means for high-throughput ad hoc networking, when the MIMO channel is used with spatial multiplexing. In both cases, concatenated DMIMO links are treated. The key contribution of this dissertation is a method of pre-synchronization of distributed single-antenna transmitters to form a virtual antenna array, in the absence of a global clock, such as a global positioning system (GPS) receiver or a network time protocol (NTP) to provide reference signals for the synchronization. Instead, the reference for synchronization comes from a packet, transmitted by the previous virtual array and simultaneously received by all the cooperative transmitters for the next hop. The method is realized for two types of modulation: narrowband non-coherent binary frequency-shift keying (NCBFSK) and wideband orthogonal frequency division multiplexing (OFDM). The pre-synchronization algorithms for transmission are designed to minimize the root-mean-square (RMS) transmit time, sampling and carrier frequency error between cooperative transmitters, with low implementation complexity. Since CCT is not supported by any existing standard or off-the-shelf radios, CT must be demonstrated by using software-defined radios (SDRs). Therefore, another contribution is a fully self-contained and real-time SDR testbed for CCT-based networking. The NCBFSK and OFDM systems have been designed and implemented in C++ and Python programming languages in the SDR testbed, providing practical performance of the CCT-based systems.

Distortion-based crest factor reduction (CFR) algorithms were studied in orthogonal frequency division multiplexing (OFDM) and multiple-input multiple-output (MIMO) OFDM systems to reduce the nonlinear distortion and improve the power efficiency of the transmitter front-end. First, definitions of peak-to-average-power ratio (PAR) were clarified based on the power efficiency improvement consideration in the MIMO-OFDM systems. Next, error vector magnitude (EVM) was used as the in-band performance-evaluating metric. Statistical analysis of EVM was performed to provide concrete thresholds for the amount of allowable distortions from each source to meet EVM requirements in the standard. Furthermore, an effective CFR technique, constrained clipping, was proposed to drastically reduce the PAR while satisfying any given in-band EVM and out-of-band spectral mask constraints. Constrained clipping has low computational complexity and can be easily extended to the multiple-user OFDM environment. Finally, signal-to-noise-and-distortion ratio (SNDR) analysis for transceiver nonlinearities in the additive white Gaussian noise channel was investigated. An analytical solution was presented for maximizing the transceiver SNDR for any given set of nonlinear transmitter polynomial coefficients. Additionally, mutually inverse pair of transceiver nonlinearities was shown to be SNDR-optimal only in the noise-free case.

[pt] Este trabalho de dissertação de mestrado apresenta os resultados obtidos com a conjunção de duas técnicas propostas para utilização em modernos sistemas de comunicações: a Modulação Espacial (Spatial Modulation - SM) e a detecção desacoplada de sinais. Na primeira parte são abordados os fundamentos teóricos da detecção de sinais com modulação espacial, uma comparação entre os sistemas MIMO (Multiple Input Multiple Output) tradicionais e os sistemas SM-MIMO, uma revisão bibliográfica sobre trabalhos previamente feitos no tema e os diferentes tipos de detectores que podem ser empregados em sistemas com modulação espacial. A seguir são abordadas diferentes técnicas para desacoplamento de sinais, as quais permitem a separação na estação radio-base dos sinais oriundos de diferentes tipos de usuários, visando simplificar e adequar o procedimento de detecção às necessidades do usuário da rede. Finalmente uma análise de desempenho, em termos da taxa de erro de bit, e complexidade computacional, em termos do número médio de flops requerido por vetor de símbolos detectado, é realizada para as diferentes associações de técnicas de desacoplamento e detectores SM enfocados neste trabalho. / [en] This work dissertation presents the results obtained from the conjunction of two proposal techniques for the use in modern systems of communications: the Spatial Modulation and the Decoupling Signal Detection. In the first part are discussed the theorical bases of the signal detection with Spatial Modulation, a comparison between the traditional MIMO systems and the SM-MIMO systems, a bibliographical review about previousworks in the topic and the different kinds of detectors that can be used in systems with Spatial Modulation. Then the different techniques of signal decoupling are discussed, which allow the separation in the radio base station of the signals coming from the different classes of users, to simplify and adapt the process of detection and the requirements of the user in the network. Finally a performance analysis in terms of the bit error rate and computational complexity in terms of average number of flops required fot the vector of symbols detected, is done for the studied detectors in the dissertation, using the same different techniques of decoupling studied in this work.