The next-generation wireless technologies are currently being researched to address the ever-increasing demands for higher data rates, massive connectivity, improved reliability, and extended coverage. Recently, massive multiple-input multiple-output (MIMO) has gained significant attention as a new physical-layer transmission technology that can achieve unprecedented spectral and energy efficiency gains via aggressive spatial multiplexing. Thus, massive MIMO has been one of the key enabling technologies for the fifth-generation and subsequent wireless standards. This dissertation thus focuses on developing a system, channel, and signal models by considering the practical wireless transmission impairments for massive MIMO systems, and ascertaining the viability of massive MIMO in fulfilling massive access, improved spectrum, enhanced security, and energy efficiency requirements. Specifically, new system and channel models, pilot sequence designs and channel estimation techniques, secure transmit/receive beamforming techniques, transmit power allocation schemes with enhanced security provisions, energy efficiency, and user fairness, and comprehensive performance analysis frameworks are developed for massive MIMO-aided non-orthogonal multiple access (NOMA), cognitive spectrum-sharing, and wireless relaying architectures.Our first work focuses on developing physical-layer transmission schemes for NOMA-aided massive MIMO systems. A spatial signature-based user-clustering and pilot allocation scheme is first formulated, and thereby, a hybrid orthogonal multiple access (OMA)/NOMA transmission scheme is proposed to boost the number of simultaneous connections. In our second work, the viability of invoking downlink pilots to boost the achievable rate of NOMA-aided massive MIMO is investigated. The third research contribution investigates the performance of underlay spectrum-sharing massive MIMO systems for reverse time division duplexing based transmission strategies, in which primary and secondary systems concurrently operate in opposite directions. Thereby, we show that the secondary system can be operated with its maximum average transmit power independent of the primary system in the limit of infinity many primary/secondary base-station antennas. In our fourth work, signal processing techniques, power allocation, and relay selection schemes are designed and analyzed for massive MIMO relay networks to optimize the trade-off among the achievable user rates, coverage, and wireless resource usage. Finally, the cooperative jamming and artificial noise-based secure transmission strategies are developed for massive MIMO relay networks with imperfect legitimate user channel information and with no channel knowledge of the eavesdropper. The key design criterion of the aforementioned transmission strategies is to efficiently combine the spatial multiplexing gains and favorable propagation conditions of massive MIMO with properties of NOMA, underlay spectrum-sharing, and wireless relay networks via efficient signal processing.

Underlay signaling is a robust physical layer technique, allowing for transmitting a very low power signal in conjunction with the primary signals across the entire frequency band of the primary signals. The secondary users of the secondary network (i.e., a wireless network consisting of primary and secondary networks) primarily utilize the underlay, which increases spectral efficiency and improves the network capacity. This thesis focuses on underlay signaling in the context of the cellular (primary) network, where the underlay is an auxiliary channel made available to the primary users and the network, that is, the base stations and users of the cellular network. The current fifth-generation (5G) cellular networks are constructed using Orthogonal Frequency Division Multiplexing (OFDM) modulation. Hence, this thesis delves into the study of underlay coexistence with OFDM, specifically 5G, by performing extensive simulations and analytical analysis and investigating the impact of underlay signaling on the throughput performance of 5G networks. We develop the underlay signaling based on the frequency-domain spread spectrum and add the underlay signal prior to the Inverse Fast Fourier Transform (IFFT) operation of OFDM. Furthermore, we present a real 5G setup built on the srsRAN project, where we showcase a proof-of-concept demonstration of underlay coexistence with the 5G over the air, where the 5G base station transmits both 5G NR and underlay signal simultaneously. Through our research, we conclusively demonstrate that a low-data rate underlay signal can be successfully transmitted alongside the existing 5G signal. Our study concludes by carefully selecting the appropriate design parameters, such as the signal-to-interference power level (5G power in relation to underlay), spreading factor, and coding gain at which we can reliably detect and decode underlay signals having no impact on the 5G performance. The integration of underlay in 5G brings forth a multitude of benefits using underlay for military and tactical applications, massive Machine Type Communications (mMTC) alongside Ultra-Reliable Low Latency Communications (URLLC), and the offloading of crucial control information of 5G to the underlay channel. Thus, this underlay operates as a low-data rate error-free conduit, with the potential to provide Low Probability of Interception (LPI) and Low Probability of Detection (LPD) attributes and heightened reliability while concurrently transmitting with the 5G NR, bolstering the overall effectiveness of the communication. / Master of Science / Underlay signaling is a technique that allows for transmitting a low-power signal alongside the primary signals, occupying the entire frequency band of the primary signals. The secondary users of the secondary network (i.e., a wireless network consisting of primary and secondary networks) primarily utilize the underlay, which increases spectral efficiency and improves the network capacity. This thesis focuses on underlay signaling in the context of cellular (primary) networks where the underlay is an auxiliary channel made available to the primary users and network, that is, the base stations and users of the cellular network. The current fifth-generation (5G) cellular networks are constructed using Orthogonal Frequency Division Multiplexing (OFDM) modulation. OFDM is a multicarrier modulation scheme that divides the available frequency band into multiple narrow subcarriers, each carrying a portion of the data. The key advantage of OFDM is its ability to combat frequency-selective fading, where different frequencies experience different levels of fading and interference. By using many closely spaced sub-carriers, OFDM can effectively mitigate the impact of fading, allowing for robust and reliable communication even in challenging channel conditions. Thus, this thesis investigates the co-existence of underlay signaling and OFDM in 5G. We develop the underlay signaling based on the frequency-domain spread spectrum. Extensive simulations and analytical analysis are performed to understand the impact of underlay signaling on OFDM performance in terms of bit error rates and throughput. Additionally, a real 5G setup is presented, demonstrating a proof-of-concept of underlay co-existence with 5G NR, where the 5G base station transmits both 5G NR and underlay signal simultaneously. Through the research, it is conclusively demonstrated that a low-data rate error-free underlay signal can be successfully transmitted alongside the existing 5G signal. The integration of underlay in 5G brings forth a multitude of benefits using underlay for military and tactical applications, massive Machine Type Communications (mMTC) alongside Ultra-Reliable Low Latency Communications (URLLC), and the offloading of crucial control information of 5G to the underlay channel. Thus, this underlay operates as a low-data rate error-free conduit, characterized by its low interception and low detection attributes, enhancing reliability while concurrently transmitting with 5G NR, bolstering the overall effectiveness of the communication.

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Relay-assisted cooperative communication exploits spatial diversity to combat wireless fading, and is an appealing technology for next generation wireless systems. Several relay cooperation protocols have been proposed in the literature. In amplify-and-forward (AF)relaying, which is the focus of this thesis, the relay amplifies the signal it receives from the source and forwards it to the destination. AF has been extensively studied in the literature on account of its simplicity since the relay does not need to decode the received signal. We propose a novel optimal relaying policy for two-hop AF cooperative relay systems. In this, an average power-constrained relay adapts its gain and transmit power to minimize the fading-averaged symbol error probability (SEP) at the destination. Next, we consider a generalization of the above policy in which the relay operates as an underlay cognitive radio (CR). This mode of communication is relevant because it promises to address the spectrum shortage constraint. Here, the relay adapts its gain as a function of its local channel gain to the source and destination and also the primary such that the average interference it causes to the primary receiver is also constrained. For both the above policies, we also present near-optimal, simpler relay gain adaptation policies that are easy to implement and that provide insights about the optimal policies. The SEPs and diversity order of the policies are analyzed to quantify their performance. These policies generalize the conventional fixed-power and fixed-gain AF relaying policies considered in cooperative and CR literature, and outperform them by 2.0-7.7 dB. This translates into significant energy savings at the source and relay, and motivates their use in next generation wireless systems.

La Radio Cognitive (CR) est une technique prometteuse pour assurer une utilisation efficace du spectre. Elle permet à un utilisateur non licencié appelé utilisateur secondaire (SU) de coexister avec un utilisateur agréé appelé utilisateur primaire (PU) sans dégrader les performances du dernier. Dans un système de CR, le SU a la capacité de s'adapter à son environnement afin de détecter des trous de fréquences possibles dans le spectre et transmettre dans ces trous sous certaines contraintes de manière à augmenter le débit total. Par ailleurs, l'allocation des ressources dans les systèmes CR forme l'un des scénarios étudiés les plus courantes en particulier pour des transmissions à porteuses multiples.Dans cette thèse, nous étudions le problème d'allocation des ressources pour un système CR à multi-utilisateur pour une transmission de liaison montante. On considère le scénario underlay où le SU est autorisé à coexister avec le PU à condition que l'interférence causé au PU soit inférieure à un seuil prédéfini. Nous appliquons deux techniques de décodage, l'annulation successive d'interférence (SIC) et le codage à superposition (SC), au SU afin de maximiser le débit secondaire.Dans une première étape, le scénario mono-utilisateur est étudié, en supposant que les informations d'état de canal sont connues parfaitement au SU. Nous évaluons la performance du système en proposant un algorithme de décodage adaptatif où le SU peut soit traiter l'interférence venant du primaire comme du bruit, ou bien appliquer le SIC ou SC. Nous étudions le problème d'allocation de puissance en tenant compte du budget de puissance et des contraintes de seuil d'interférence. Une solution générale pour le problème d'optimisation est proposé. L'analyse des simulations et les résultats théoriques montrent que l'algorithme proposé assure une augmentation sur le débit total du système.Ensuite, le scénario multi-utilisateurs secondaires est étudié, où plusieurs utilisateurs sont autorisés à exister dans la cellule secondaire. Les problème d'allocation de puissance et de sous-porteuses sont détaillés dans le but de maximiser le débit. Nous mettons en évidence les avantages de l'algorithme adaptatif dans le cas multi-utilisateur, qui comprend trois phases. La première étape comprend la sélection adaptative de la stratégie de décodage au niveau du récepteur secondaire. La deuxième étape décrit l'attribution de sous-porteuses parmi les différents utilisateurs. Enfin, la troisième étape détaille la répartition optimale du budget de puissance disponible sur les utilisateurs.Cependant, la connaissance parfaite du canal nécessite des mesures de canal parfait au niveau du récepteur et un lien de rétroaction parfaite pour envoyer ces informations à l'émetteur, ce qui peut être impossible à mettre en œuvre. Ainsi, nous étudions aussi le scénario mono-utilisateur en supposant que juste la connaissance statistique des gains de canaux primaires est disponible au SU. Nous détaillons les expressions analytiques pour les probabilités de panne et nous résolvons le problème d'optimisation non-convexe en utilisant un algorithme d'approximation séquentielle. Les simulations montrent que l'algorithme proposé est efficace et robuste.Enfin, nous proposons un nouveau modèle de système où le récepteur secondaire peut agir comme un nœud de relayage Full-Duplex (FD) afin de maximiser le débit primaire. Le scénario proposé est d'abord étudié pour un schéma de modulation à mono-porteuse dans les cas Amplify-and-Forward (AF) et Decode-and-Forward (DF). Les contraintes pour appliquer le SIC et pour le relayage sont déterminés et les nouveaux débits réalisables sont spécifiés de telle sorte que le nœud de relayage relaie si le nouveau débit atteignable est meilleur que celui obtenu sans relayage. En outre, le scénario FD avec DF est étudié avec la modulation multi-porteuse et les performances de ce modèle sont évaluées. Une amélioration importante sur le débit primaire est affiché. / Cognitive Radio (CR) is a promising technique for efficient spectrum utilization. The CR technology permits an unlicensed user called Secondary User (SU) to coexist with the licensed user called Primary User (PU) without degrading his performance. In a CR system, the SU has the ability to sense and adapt to his environment in order to detect possible frequency holes in the wireless spectrum and transmit in it under some constraints so as to increase the total data rate. Besides, resource allocation in CR systems is one of the most common studied scenarios especially for multi-carrier transmissions, with the aim to maximize the system throughput.In this thesis, we investigate the resource allocation problem for an uplink multi-user underlay CR system where the SU is allowed to coexist with the PU provided that the interference caused to the PU is below a predefined threshold. We apply two decoding techniques, Successive Interference Cancellation (SIC) and Superposition Coding (SC), at the SU in order to maximize the secondary rate. In a first step, the single-user scenario is studied, assuming perfect channel state information (CSI) at the SU. We evaluate the performance of the system by proposing an adaptive decoding algorithm where the SU can either treat the interference as noise or perform SIC or SC. We investigate the power allocation problem taking into account the power budget and the interference threshold constraints. A general solution for the power optimization problem in an uplink underlay CR system is proposed. Both theoretical analysis and simulation results show that the proposed algorithm achieves higher sum rate than classical algorithms, providing high-enough data rates for the secondary system at the expense of a very low degradation of the primary system's rate.Then, the secondary multi-user scenario is investigated, where multiple users are allowed to exist in the secondary cell. Power and subcarrier allocation problems are detailed in order to maximize the secondary rate. We highlight the benefits of the proposed multi-user adaptive algorithm which encompasses three phases. The first step includes the adaptive selection of the decoding strategy at the secondary receiver. The second step describes the subcarrier allocation among the different users. Finally, the third step details the optimal distribution of the available power budget on the users.However, perfect channel knowledge requires perfect channel measurements at the receiver and a perfect feedback link to send this channel information to the transmitter, which may be impractical to implement. Thus, we also study the single-user scenario assuming that only statistical CSI of channel gains between the primary transmitter and both primary and secondary receivers is available at the SU. We detail the analytical expressions for the outage probabilities and then we solve the non-convex optimization problem using a sequential approximation algorithm. simulations show that the proposed algorithm is efficient and robust with statistical CSI. This work can be easily extended to the multi-user case.Finally, we propose a new system model where the secondary receiver acts as a Full-Duplex (FD) relay node in order to maximize the primary rate and thus the total system rate. The proposed scenario is first studied for single-carrier modulation scheme for both Amplify-and-Forward (AF) and Decode-and-Forward (DF) relaying protocols. The constraints to apply SIC and to relay are determined and the new achievable rates are specified such that the relay node relays whenever the new achievable rate is better than the one achieved without relying. Furthermore, the performance of the DF relaying scheme in the FD mode is evaluated for multi-carrier modulation. The performance of the proposed system model is evaluated via simulations and an important improvement of the primary achievable rate and thus of the total system rate is shown.

Due to the rapid development of wireless communications together with the inflexibility of the current spectrum allocation policy, radio spectrum becomes more and more exhausted. One of the critical challenges of wireless communication systems is to efficiently utilize the limited frequency resources to be able to support the growing demand of high data rate wireless services. As a promising solution, cognitive radios have been suggested to deal with the scarcity and under-utilization of radio spectrum. The basic idea behind cognitive radios is to allow unlicensed users, also called secondary users (SUs), to access the licensed spectrum of primary users (PUs) which improves spectrum utilization. In order to not degrade the performance of the primary networks, SUs have to deploy interference control, interference mitigating, or interference avoidance techniques to minimize the interference incurred at the PUs. Cognitive radio networks (CRNs) have stimulated a variety of studies on improving spectrum utilization. In this context, this thesis has two main objectives. Firstly, it investigates the performance of single hop CRNs with spectrum sharing and opportunistic spectrum access. Secondly, the thesis analyzes the performance improvements of two hop cognitive radio networks when incorporating advanced radio transmission techniques. The thesis is divided into three parts consisting of an introduction part and two research parts based on peer-reviewed publications. Fundamental background on radio propagation channels, cognitive radios, and advanced radio transmission techniques are discussed in the introduction. In the first research part, the performance of single hop CRNs is analyzed. Specifically, underlay spectrum access using M/G/1/K queueing approaches is presented in Part I-A while dynamic spectrum access with prioritized traffics is studied in Part I-B. In the second research part, the performance benefits of integrating advanced radio transmission techniques into cognitive cooperative radio networks (CCRNs) are investigated. In particular, opportunistic spectrum access for amplify-and-forward CCRNs is presented in Part II-A where collaborative spectrum sensing is deployed among the SUs to enhance the accuracy of spectrum sensing. In Part II-B, the effect of channel estimation error and feedback delay on the outage probability and symbol error rate (SER) of multiple-input multiple-output CCRNs is investigated. In Part II-C, adaptive modulation and coding is employed for decode-and-forward CCRNs to improve the spectrum efficiency and to avoid buffer overflow at the relay. Finally, a hybrid interweave-underlay spectrum access scheme for a CCRN is proposed in Part II-D. In this work, the dynamic spectrum access of the PUs and SUs is modeled as a Markov chain which then is utilized to evaluate the outage probability, SER, and outage capacity of the CCRN.

In the literature, Cognitive radio (CR) as well as full-duplex (FD) communication technologies are proposed to increase the spectrum efficiency. The main contribution of this thesis is to introduce prediction and estimation techniques with low control overhead, and use the predicted or estimated information in resource allocation in CR networks, both in the overlay networks and the underlay networks. Prediction and estimation are important in increasing the data rate and keeping the interference at a low level. In the overlay scheme, I modeled the primary user (PU) traffic characteristics of the channels using the Probabilistic Suffix Tree (PST) algorithm. Then using this PST algorithm, I introduced a frequency hopping based control channel and derived its theoretical properties. Then I proposed two methods for selecting a channel set for transmission, which took into account both the PU channel usage statistics and, secondary user (SU) channel usage statistics as perceived by an SU of interest. The first scheme selected channels having the highest probability of successful transmission, while the second calculated a net reward using a marked Markov chain. Then using simulations, I showed that our scheme caused acceptable interference to the PUs and has better throughput performance, compared to a scheme selecting channels randomly. Then I proposed two joint channel assignment and power allocation schemes for a bi-directional FD underlay CR network with network assistance. The first scheme used the information on the number of total SU pairs present in the network. In the second scheme, I used least squares based estimation and Kalman filtering to estimate the interference at the monitoring stations using the local interference. It reduced the control overhead of keeping track of active SUs. In both of these schemes each SU pair decided on the channels to be used in the half-duplex mode and the full-duplex mode using local information. This joint optimization was done running channel assignment and power allocation algorithms alternatively. In the power allocation problem, I used a technique called monotonic optimization. After simulating both of these schemes I showed that the scheme based on estimation performs satisfactorily given that it has less control overhead. / October 2016

The Renaissance theorist Gioseffo Zarlino and his theoretical treatise Le istitutioni harmoniche were a vital link to the future of theory. His polyphonic music and ten text underlay rules are representative of the new music of the Venetian School, which was headed by his mentor Adrian Willaert. Examination of Zarlino's thirteen extant madrigals provides us with a direct example of these rules and the secular style of the Venetian School, who strived to elevate their secular works to that of sacred music. The style was inspired by Pietro Bembo's Petrarchan revival, in which Renaissance composers utilized medieval Petrarchan texts or wrote new texts in the Petrarchan style. The texts were set to music which was composed to express the emotions of the texts. Zarlino accomplished this through the selection of major, minor, and diminished sonorities, which began the move to major-minor tonality in the history of Western music.

Simultaneous operation of different wireless applications in the same geographical region and the same frequency band gives rise to undesired interference issues. Since licensed (primary) applications have been granted priority access to the frequency spectrum, unlicensed (secondary) services should avoid imposing interference on the primary system. In other words, secondary system’s activity in the same bands should be in a controlled fashion so that the primary system maintains its quality of service (QoS) requirements. In this thesis, we consider collocated point-to-multipoint primary and secondary networks that have simultaneous access to the same frequency band. Particularly, we examine three different levels at which the two networks may coexist: pure interference, asymmetric co-existence, and symmetric co-existence levels. At the pure interference level, both networks operate simultaneously regardless of their interference to each other. At the other two levels, at least one of the networks attempts to mitigate its interference to the other network by deactivating some of its users. Specifically, at the asymmetric co-existence level, the secondary network selectively deactivates its users based on knowledge of the interference and channel gains, whereas at the symmetric level, the primary network also schedules its users in the same way. Our aim is to derive optimal sum-rates (i.e., throughputs) of both networks at each co-existence level as the number of users grows asymptotically and evaluate how the sum-rates scale with the network size. In order to find the asymptotic throughput results, we derive two propositions; one on the asymptotic behaviour of the largest order statistic and one on the asymptotic behaviour of the sum of lower order statistics. As a baseline comparison, we calculate primary and secondary sum-rates for the time division (TD) channel sharing. Then, we compare the asymptotic secondary sum-rate in TD to that under simultaneous channel sharing, while ensuring the primary network maintains the same sum-rate in both cases. Our results indicate that simultaneous channel sharing at both asymmetric and symmetric co-existence levels can outperform TD. Furthermore, this enhancement is achievable when user scheduling in uplink mode is based only on the interference gains to the opposite network and not on a network’s own channel gains. In other words, the optimal secondary sum-rate is achievable by applying a scheduling strategy, referred to as the least interference strategy, for which only the knowledge of interference gains is required and can be performed in a distributed way.

Simultaneous operation of different wireless applications in the same geographical region and the same frequency band gives rise to undesired interference issues. Since licensed (primary) applications have been granted priority access to the frequency spectrum, unlicensed (secondary) services should avoid imposing interference on the primary system. In other words, secondary system’s activity in the same bands should be in a controlled fashion so that the primary system maintains its quality of service (QoS) requirements. In this thesis, we consider collocated point-to-multipoint primary and secondary networks that have simultaneous access to the same frequency band. Particularly, we examine three different levels at which the two networks may coexist: pure interference, asymmetric co-existence, and symmetric co-existence levels. At the pure interference level, both networks operate simultaneously regardless of their interference to each other. At the other two levels, at least one of the networks attempts to mitigate its interference to the other network by deactivating some of its users. Specifically, at the asymmetric co-existence level, the secondary network selectively deactivates its users based on knowledge of the interference and channel gains, whereas at the symmetric level, the primary network also schedules its users in the same way. Our aim is to derive optimal sum-rates (i.e., throughputs) of both networks at each co-existence level as the number of users grows asymptotically and evaluate how the sum-rates scale with the network size. In order to find the asymptotic throughput results, we derive two propositions; one on the asymptotic behaviour of the largest order statistic and one on the asymptotic behaviour of the sum of lower order statistics. As a baseline comparison, we calculate primary and secondary sum-rates for the time division (TD) channel sharing. Then, we compare the asymptotic secondary sum-rate in TD to that under simultaneous channel sharing, while ensuring the primary network maintains the same sum-rate in both cases. Our results indicate that simultaneous channel sharing at both asymmetric and symmetric co-existence levels can outperform TD. Furthermore, this enhancement is achievable when user scheduling in uplink mode is based only on the interference gains to the opposite network and not on a network’s own channel gains. In other words, the optimal secondary sum-rate is achievable by applying a scheduling strategy, referred to as the least interference strategy, for which only the knowledge of interference gains is required and can be performed in a distributed way.