We examine the effect of precoding on OFDM systems. The precoding operation, which is also known as constellation rotation, leads to a gain in diversity order for fading channels. In this thesis, we examine the effect of precoding for different receivers such as Maximum Likelihood (ML), Minimum Mean Squared Error (MMSE), and Zero Forcing (ZF) receivers. The diversity gain due to precoding comes at no cost of bandwidth expansion or power increase. Therefore it is an attractive and practical alternative. We also examine the precoding gain, when some reduction of rate is tolerable and compare the performance of rate reduced system with the uncoded system with the system which is coded by rateless unitary precoders, and with the hard-decision decoded BCH coded coded system.

In cooperative networks, relays cooperate and form a distributed multi-antenna system to provide spatial diversity. In order to achieve high bandwidth efficiency, distributed space-time block codes (DSTBCs) are proposed and have been studied extensively. Among all DSTBCs, this thesis focuses on the codes which are single-symbol maximum likelihood (ML) decodable and can achieve the full diversity order. This thesis presents four works on single-symbol ML decodable DSTBCs. The first work proposes the row-monomial distributed orthogonal space-time block codes (DOSTBCs). We find an upper bound of the data-rate of the row-monomial DOSTBC and construct the codes achieving this upper bound. In the second work, we first study the general DOSTBCs and derive an upper bound of the data-rate of the DOSTBC. Secondly, we propose the row-monomial DOSTBCs with channel phase information (DOSTBCs-CPI) and derive an upper bound of the data-rate of those codes. Furthermore, we find the actual row-monomial DOSTBCs-CPI which achieve the upper bound of the data-rate. In the third and fourth works of this thesis, we focus on error performance analysis of single-symbol ML decodable DSTBCs. Specifically, we study the distributed Alamouti's code in dissimilar cooperative networks. In the third work, we assume that the relays are blind relays and we derive two very accurate approximate bit error rate (BER) expressions of the distributed Alamouti's code. In the fourth work, we assume that the relays are CSI-assisted relays. When those CSI-assisted relays adopt the amplifying coefficients that was proposed in [33] and widely used in many previous publications, upper and lower bounds of the BER of the distributed Alamouti's code are derived. Very surprisingly, the lower bound indicates that the code cannot achieve the full diversity order when the CSI-assisted relays adopt the amplifying coefficients proposed in [33]. Therefore, we propose a new threshold-based amplifying coefficient and it makes the code achieve the full diversity order two. Moreover, three optimum and one suboptimum schemes are developed to calculate the threshold used in this new amplifying coefficient. / Thesis (Ph.D, Electrical & Computer Engineering) -- Queen's University, 2009-06-27 19:07:47.066

Demand for capacity in wireless communication systems has been rapidly growing world- wide. This has been driven by increasing data rate requirements of cellular mobile systems, and demand for wireless Internet and multimedia services. As the available radio spec- trum is limited, higher data rates can only be achieved by designing more efficient signaling techniques. In this thesis, we propose a new transmission scheme, which benefits from the advantages of conventional space-time trellis codes (CSTTCs) but does not have the disadvantages, especially for larger signal constellations. We achieve this by developing a new class of codes, called Multilevel Space-Time Trellis Codes (IMLSTTC). The new scheme provides a scalable and promising alternative to CSTTCs, by providing the system designer with the flexibility to choose any desired balance between code performance, complexity and throughput. The proposed scheme outperforms layered schemes at high SNRs, using a smaller number of antennas.

Abstract Broadband single-carrier modulated signals experience severe multipath distortion when propagating through the physical medium. Correcting the distortion with channel equalization is the foremost task of the detector. Prior information about the transmitted signals in the form of channel decoder feedback can significantly enhance equalization accuracy. An algorithm that iteratively performs channel decoding and equalization with prior information is generally denoted a turbo equalizer. This thesis focuses on turbo equalization with prior information using the principle of interference cancellation followed by minimum mean squared error (MMSE) filtering. Receiver algorithms, receiver convergence, and coding and modulation in the context of MMSE turbo equalization are studied. Computationally efficient versions of the receiver algorithm through approximate time-average filtering, matched filtering, square-root time-variant filtering and frequency-domain filtering are studied. The frequency-domain turbo equalizer (FDTE) is found to exhibit both superior convergence and low computational complexity among the compared equalizer algorithms. Multi-dimensional extrinsic information transfer (EXIT) charts are introduced for the purpose of tracking the convergence of the turbo equalization of layered MIMO transmissions. Generic properties of the equalizer EXIT functions defining the equalizer convergence are analyzed. The principles for detector ordering, maximum sum-rate code design and maximum rate symmetric design are derived from the properties of the multidimensional EXIT functions. Semi-analytical EXIT charts are developed for the convergence analysis of the FDTE. The effects of channel parameters and the channel code are analyzed with semi-analytical methods. A new approach for the design of irregular low-density parity-check (LDPC) codes using a convergence outage principle is proposed. A performance gain is demonstrated in a single-input multiple output (SIMO) channel over non-optimized regular LDPC codes and irregular LDPC codes optimized for the AWGN channel. The outage convergence based design, which takes advantage of the semi-analytical convergence analysis method, is also extended to layered MIMO transmissions. Quadrature amplitude modulation using multilevel bit-interleaved coded modulation (MLBICM) is studied as an alternative to regular bit-interleaved coded modulation (BICM) for highly bandwidth-efficient transmission in MMSE turbo equalized systems. A linear bit-to-symbol mapping is introduced that enables the use of a computationally efficient MMSE turbo equalizer at the receiver. The proposed coded modulation is compared with BICM in channel measurement data based simulations and found to exhibit superior robustness against changes in spatial channel parameters. An automatic repeat request (ARQ) configuration using one ARQ controller for each equally performing group of code levels is proposed. The configuration takes advantage of the unequal error protection (UEP) property of the coded modulation. The semi-analytical convergence analysis is extended to the multilevel modulated case and applied in a channel measurement based convergence evaluation. The construction of the MLBICM is found to have an inherently better convergence behavior than BICM. Finally, the outage convergence based channel code design is extended to the layered MIMO multilevel signalling case.

No description available.

By endowing the base station with hundreds of antennas and relying on spatial multiplexing, massive multiple-input-multiple-output (MIMO) allows impressive advantages in many fronts. To reduce this promising technology to reality, thorough performance analysis has to be conducted. Along this line, this work is focused on the convenient high-dimensionality of massive MIMO’s corresponding model. Indeed, the large number of antennas allows us to harness asymptotic results from Random Matrix Theory to provide accurate approximations of the main performance metrics. The derivations yield simple closed-form expressions that can be easily interpreted and manipulated in contrast to their alternative random equivalents. Accordingly, in this dissertation, we investigate and optimize the performance of massive MIMO in different contexts. First, we explore the spectral efficiency of massive MIMO in large-scale multi-tier heterogeneous networks that aim at network densification. This latter is epitomized by the joint implementation of massive MIMO and small cells to reap their benefits. Our interest is on the design of coordinated beamforming that mitigates cross-tier interference. Thus, we propose a regularized SLNR-based precoding in which the regularization factor is used to allow better resilience to channel estimation errors. Second, we move to studying massive MIMO under Line-of-Sight (LoS) propagation conditions. To this end, we carry out an analysis of the uplink (UL) of a massive MIMO system with per-user channel correlation and Rician factor. We start by analyzing conventional processing schemes such as LMMSE and MRC under training-based imperfect-channel-estimates, and then, propose a statistical combining technique that is more suitable in LoS-prevailing environments. Finally, we look into the interplay between LoS and the fundamental limitation of massive MIMO systems, namely, pilot contamination. We propose to analyze and compare the performance using single-cell and multi-cell detection methods. In this regard, the single-cell schemes are shown to produce higher SEs as the LoS strengthens, yet remain hindered by LoS-induced interference and pilot contamination. In contrast, for multi-cell combining, we analytically demonstrate that M-MMSE outperforms both single-cell detectors by generating a capacity that scales linearly with the number of antennas, and is further enhanced with LoS.

No description available.

Η έννοια της ψηφιακής αναμετάδοσης έχει μελετηθεί σαν ένα ϑεωρητικό πρόβλημα από την πλευρά της ϑεωρίας της πληροφορίας στις δεκαετίες του ’70 και ’80 όπου υπολογίστηκε η χωρητικότητα συστημάτων με ένα αναμεταδότη. Το σενάριο στο οποίο η επικοινωνία δύο τερματικών σταθμών πραγματοποείται με τη ϐοήθεια ενός τρίτου το οποίο αναλαμβάνει να αναμεταδόσει την πληροφορία, υλοποιήθηκε αρχικά στους δορυφόρους με ανακλαστική επανεκπομπή. Ενδιαφέρον, σύμφωνα με όσα γνωρίζουμε, προκαλεί το γεγονός ότι δεν υπήρχε έως πολύ πρόσφατα καμία εργασία σχετική με την ϑεωρία της αναμετάδοσης - πιο πιθανή αιτία η μη ύπαρξη σχετικών εφαρμογών. Με την ωριμότητα των ψηφιακών ασύρματων επικοινωνιών και λόγω των ϱαγδαία αυξανόμενων αναγκών για επικοινωνίες υψηλής απόδοσης, ϕαίνεται ότι έφτασε η ώρα για την ανάπτυξη ‘‘έξυπνης’’ αναμετάδοσης στο άμεσο μέλλον. Η παρούσα διδακτορική διατριβή (DD) έρχεται να συμβάλλει προς την κατεύθυνση αυ- τή και να δώσει στους μελετητές των ψηφιακών επικοινωνιών νέες τεχνικές και εργαλεία αναλύοντας και μελετώντας στο ϕυσικό επίπεδο τα ασύρματα τηλεπικοινωνιακά συστήματα (ή δίκτυα) πολλαπλών αλμάτων με μη-αναγεννητικούς αναμεταδότες δηλ. συστήματα στα οποία το σήμα εκπέμπεται από τον πηγαίο κόμβο και ϕθάνει στον κόμβο προορισμού διαμέσου ενός ή περισσοτέρων αναμεταδοτών. Με την τεχνική αυτή καταπολεμούμε τους δύο ϐασικούς παράγοντες υποβάθμισης του εκπεμπόμενου σήματος που είναι η μειωμένη μέση ισχύς λήψης λόγω απόστασης ή/και εμποδίων, και οι διακυμάνσεις του σήματος στη λήψη του, εξαιτίας του ϕαινομένου των διαλείψεων. Βασικός σκοπός της DD είναι η αξιολόγηση των επιδόσεων των συστημάτων πολλαπλών αλμάτων, που λειτουργούν σε περιβάλλον διαλείψεων Rayleigh ή Nakagami-m, με δείκτες επιδόσεων όπως ο μέσος λό- γος σήματος προς ϑόρυβο (ΛΣΘ), η πιθανότητα διακοπής της επικοινωνίας (ΠDΕ) και η μέση πιθανότητα σφάλματος bit (ΜΠΣΒ). Για να επιτευχθούν τα παραπάνω στα πολυαλ- ματικά συστήματα, απαιτείται η στατιστική μελέτη του απ’ άκρο-σε-άκρο ΛΣΘ στην έξο- δο του κόμβου προορισμού για την εξαγωγή σημαντικών στατιστικών συναρτήσεων όπως της συνάρτησης πυκνότητας πιθανότητας (ΣΠΠ), της συνάρτησης αθροιστικής πιθανότητας (ΣΑΠ), της ϱοπο-γεννήτριας συνάρτησης (ΡΓΣ) και των ϱοπών. Οι δείκτες επίδοσης παρουσιάζονται είτε σε κλειστές μαθηματικές μορφές οι οποίες εξάγουν άμεσα αποτελέ- σματα, είτε σε αναλυτικές μορφές για τις οποίες η χρήση της αριθμητικής ολοκλήρωσης είναι απαραίτητη μέσω γνωστών μαθηματικών λογισμικών όπως MATHEMATICA ή MAPLE. Παράλληλα, όπου απαιτείται, παρουσιάζονται αποτελέσματα προσομοίωσης Monte Carlo για την επαλήθευση των αριθμητικών αποτελεσμάτων. Λαμβάνοντας υπόψην όλα τα παραπάνω, ερευνάται ένα σύστημα N αλμάτων σε περι- ϐάλλον διαλείψεων Nakagami-m και παράγονται τόσο σημαντικά αποτελέσματα για την επίδοσή τους όσο και ένα καινοτόμο στατιστικό ϑεώρημα για τη ΡΓΣ τυχαίων μεταβλητών Γάμμα. Η επίδοση των συστημάτων αυτών αξιολογείται για μη-αναγεννητικούς αναμε- ταδότες και συγκεκριμένα, τόσο για αναμεταδότες μεταβλητού κέρδους (ΑΜΚ) δηλ. το κέρδος τους εξαρτάται από την εκτίμηση της κατάστασης του καναλιού (ή κέρδος κανα- λιού) στην είσοδό τους, όσο και για αναμεταδότες σταθερού κέρδους (ΑΣΚ). Επίσης στη DD προτείνεται ένα νέος τύπου μη-αναγεννητικού αναμεταδότη, ο αναμεταδότης συνδυα- σμένου κέρδους (ΑΣυΚ), του οποίου η επίδοση εξετάζεται σε ένα σύστημα διπλού άλματος (δηλ. σ’ ένα σύστημα με έναν αναμεταδότη). Η επίδοσή του συγκρίνεται με αυτή του ΑΜΚ. Η επίδοση του ΑΣυΚ εμφανίζεται να είναι καλύτερη σε κάποιες περιπτώσεις απ’ αυτήν του ΑΜΚ. Ιδιαίτερη ϐαρύτητα δίνεται τέλος και στη μελέτη πολυαλματικών συστημάτων επικοινω- νίας με διαφορική συνεργασία χρηστών. Τα συστήματα αυτά διαφέρουν από τα συμβατικά πολυαλματικά διότι εκμεταλλεύονται τα πλεονεκτήματα της ‘‘εικονικής’’ διαφορικής εκ- πομπής στον πηγαίο κόμβο και τη διαφορική λήψη στον κόμβο προορισμού. Οι δείκτες επίδοσης εξετάζονται είτε για συστήματα διαφορικής συνεργασίας ενός χρήστη, είτε για πολλούς χρήστες με διαφορικό δέκτη συνδυασμού επιλογής ή μεγίστου λόγου στον κόμβο προορισμού, αντίστοιχα. / The concept of digital relaying has been studied as a theoretical problem from a network information theory perspective in 70’s and 80’s, and capacity regions of simple relaying channels have been evaluated. The scenario where the communication between two terminal is achieved with the help of a third terminal, was firstly implemented in bentpipe satellites. To the best of our knowledge, there has been no other analytical study on this concept until very recently due to the fact that there were no foreseeable applications at that time. With the maturity of digital wireless technologies and with the overwhelming demand for high data rate coverage, it seems that time has finally arrived for the implementation of intelligent relaying. The present PhD thesis contributes in that direction and gives to researchers of digital communications new techniques and smart tools by analyzing and studying multihop wireless communications systems in physical layer. In multihop systems, the source terminal transmits a signal which arrives to the destination terminal via a number of relays. By applying relayed transmission we mitigate two main reasons that causes Quality of Service degradation of the received signal, which are the low average receive power, induced by the presence of obstacles or by long distance, or due to the fluctuations in the received signal induced by fading effects. The main subject of this PhD is the evaluation of the performance metrics of multihop wireless communications systems, operating over Rayleigh or Nakagamim fading channels such as average signaltonoise ratio (SNR), outage probability and average biterror rate. To achieve this, the statistics of the equivalent endtoend SNR at the output of the destination terminal is required and specifically the probability density function, the cumulative distribution function, the moments and moment generating function (MGF). The performance metrics are presented either in closed forms giving direct results or in analytical ones where the results are extracted via numerical integration with the use of standard mathematical software packages such as MATHEMATICA or MAPLE. Additionally, Monte Carlo simulation results are also presented for the verification of the numerical results. Considering all the above, a multihop system with Nhops over Nakagamim environment is studied, and important performance results are derived. Also, a novel statistical result regarding the MGF of the product of rational powers of Gamma random variables is presented for the first time in the technical literature. The performance metrics of the multihop system are evaluated for nonregenerative relays and specifically, for both channel state information (CSI)based and fixed gain relays. Moreover, in this PhD thesis a new type of relay is presented, the combined gain relay (CGR), and its performance is studied in dualhop systems. The performance of the CGRs is compared to CSIbased ones whose amplification gain depends on the channel state at their input. It is interesting that CGR performs better in some situations than CSI ones. Finally, we concentrate on multihop wireless communications systems with cooperative diversity. Cooperative diversity systems differ from conventional multihop ones since exploits the benefits of virtual transmit diversity in the source terminal and diversity reception in the destination terminal. Performance analysis is conducted for cooperative diversity systems with one or more users (relays) and selection combiner or maximal ratio combiner at the destination terminal, correspondingly.

International Telemetering Conference Proceedings / October 25-28, 1999 / Riviera Hotel and Convention Center, Las Vegas, Nevada / In this paper, orthogonal wavelets are employed to produce multiscale signaling. It is shown that signaling using these functions is bandwidth efficient compared other signaling schemes, including SFSK and GMSK. For signaling in Rician fast fading channel, it is also shown that scaling functions is superior in term of achieving low level of probability of error. Even for multiscale signaling, the level probability of error achieved by using wavelet is lower than conventional flat-top signaling. The benefits are largest for channels with small B(D)T , in which the degradation due to fading is most severe.

In this thesis, we investigate the ergodic capacity under several power adaption schemes, including optimal power and rate algorithm (OPRA), optimal rate algo rithm (ORA), channel inversion (CI), and truncated channel inversion (TCI), over fluctuating two-ray (FTR) fading channels and Fisher-Snedecor F fading channels. After some mathematical manipulations, the exact expressions for the EC under those power adaption schemes are derived. To simplify the expressions and also get some insights from the analysis, the corresponding asymptotic expressions for the EC are also derived in order to show the slope and power offset of the EC in the high signal-to-noise ratio (SNR) region. These two metrics, i.e., slope and power offset, govern the EC behaviour in the high SNR region. Specifically, from the derived asymptotic expressions, we find that the slope of the EC of OPRA and ORA over FTR fading channels is always unity with respect to the average SNR in the log-scale in high SNRs, while the asymptotic EC of the TCI method is not a line function in the log-scale. For the Fisher-Snedecor F fading channel, the slope of asymptotic EC under OPRA, ORA, and CI (m > 1) schemes is unity in the log-scale, where m is the fading parameter. The slope of the TCI method depends on m, i.e., unity for m > 1 and m for m > 1, while the asymptotic EC of TCI is not a line function for m = 1. Finally, Monte-Carlo simulations are used to demonstrate the correctness of the derived expressions.