A successive interference cancellation (SIC) structure is proposed for multiuser interference cancellation (MUI) due to carrier frequency offsets (CFOs) in the uplink of orthogonal frequency division multiple access (OFDMA) systems. The proposed architecture adopts a circular convolution to suppress the impacts caused by CFOs. This paper demonstrates that, with 2 iterations, the SIC has better performance than that of the parallel interference cancellation (PIC), but system complexity is only 1/2K, where K is the number of users in the uplink of OFDMA system. This study also shows that system complexity can be significantly reduced if proper approximation is made.

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In the first part of this dissertation, a novel medium access protocol for the Internet of Thing (IoT) networks is introduced. The Internet of things (IoT), which is the network of physical devices embedded with sensors, actuators, and connectivity, is being accelerated into the mainstream by the emergence of 5G wireless networking. This work presents an uncoordinated non-orthogonal random-access protocol, which is an enhancement to the recently introduced slotted ALOHA- NOMA (SAN) protocol that provides high throughput, while being matched to the low complexity requirements and the sporadic traffic pattern of IoT devices. Under ideal conditions it has been shown that slotted ALOHA-NOMA (SAN), using power- domain orthogonality, can significantly increase the throughput using SIC (Successive Interference Cancellation) to enable correct reception of multiple simultaneous transmitted signals. For this ideal performance, the enhanced SAN receiver adaptively learns the number of active devices (which is not known a priori) using a form of multi-hypothesis testing. For small numbers of simultaneous transmissions, it is shown that there can be substantial throughput gain of 5.5 dB relative to slotted ALOHA (SA) for 0.07 probability of transmission and up to 3 active transmitters. As a further enhancement to SAN protocol, the SAN with beamforming (BF-SAN) protocol was proposed. The BF-SAN protocol uses beamforming to significantly improve the throughput to 1.31 compared with 0.36 in conventional slotted ALOHA when 6 active IoT devices can be successfully separated using 2×2 MIMO and a SIC (Successive Interference Cancellation) receiver with 3 optimum power levels. The simulation results further show that the proposed protocol achieves higher throughput than SAN with a lower average channel access delay. In the second part of this dissertation a novel Machine Learning (ML) approach was applied for proactive mobility management in 5G Virtual Cell (VC) wireless networks. Providing seamless mobility and a uniform user experience, independent of location, is an important challenge for 5G wireless networks. The combination of Coordinated Multipoint (CoMP) networks and Virtual- Cells (VCs) are expected to play an important role in achieving high throughput independent of the mobile’s location by mitigating inter-cell interference and enhancing the cell-edge user throughput. User- specific VCs will distinguish the physical cell from a broader area where the user can roam without the need for handoff, and may communicate with any Base Station (BS) in the VC area. However, this requires rapid decision making for the formation of VCs. In this work, a novel algorithm based on a form of Recurrent Neural Networks (RNNs) called Gated Recurrent Units (GRUs) is used for predicting the triggering condition for forming VCs via enabling Coordinated Multipoint (CoMP) transmission. Simulation results show that based on the sequences of Received Signal Strength (RSS) values of different mobile nodes used for training the RNN, the future RSS values from the closest three BSs can be accurately predicted using GRU, which is then used for making proactive decisions on enabling CoMP transmission and forming VCs. Finally, the work in the last part of this dissertation was directed towards applying Bayesian games for cell selection / user association in 5G Heterogenous networks to achieve the 5G goal of low latency communication. Expanding the cellular ecosystem to support an immense number of connected devices and creating a platform that accommodates a wide range of emerging services of different traffic types and Quality of Service (QoS) metrics are among the 5G’s headline features. One of the key 5G performance metrics is ultra-low latency to enable new delay-sensitive use cases. Some network architectural amendments are proposed to achieve the 5G ultra-low latency objective. With these paradigm shifts in system architecture, it is of cardinal importance to rethink the cell selection / user association process to achieve substantial improvement in system performance over conventional maximum signal-to- interference plus noise ratio (Max-SINR) and Cell Range Expansion (CRE) algorithms employed in Long Term Evolution- Advanced (LTE- Advanced). In this work, a novel Bayesian cell selection / user association algorithm, incorporating the access nodes capabilities and the user equipment (UE) traffic type, is proposed in order to maximize the probability of proper association and consequently enhance the system performance in terms of achieved latency. Simulation results show that Bayesian game approach attains the 5G low end-to-end latency target with a probability exceeding 80%.

Interference limits the throughput of modern wireless communication networks, and thus the successful mitigation of interference can have a significant impact on network performance. Successive interference cancellation (SIC) has emerged as a promising physical layer method, where multiple packets received simultaneously need not be treated as a ``collision'' requiring retransmission; rather, under certain conditions, all of the packets can be decoded. Obviously, using SIC can thus serve as an important design element that can provide higher performance for the network. However, it also requires a rethinking of the way that traditional routing and scheduling algorithms, which are designed for a traditional physical layer, are developed. In order to consider routing and scheduling over a physical layer employing SIC, some tools such as the oft-employed conflict graph need to be modified. In particular, a notion of links interfering with other links ``indirectly'' is required, and this issue has been ignored in many past works. Therefore, considering the dependencies and interferences between links, a joint routing and scheduling algorithm that employs an understanding of the SIC that will be employed at the physical layer is presented and shown to surpass previous algorithms. We know that the maximum throughput scheduling problem is NP-hard. On the other hand, even if we can reach maximum throughput scheduling, while being throughput efficient, it can result in highly unfair rates among the users. Hence, proportional fairness is developed in the proposed algorithm.

Les communications sans fils sont devenues un outil fondamental pour les sociétés modernes. Les réseaux cellulaires sont le moyen préféré pour l’accès à Internet. L’augmentation de la capacité du réseau est étroitement liée au problème des interférences. Les réseaux coopératifs ont été largement étudiés dans les années récentes. Cette thèse porte sur deux techniques de coopération dans la voie descendante :La première partie étudie les effets de quantification et délais sur les informations de retour nécessaires pour la mise en opération des différentes techniques d’émission coordonnée, connues sous le nom de CoMP (Coordinated Multipoint Transmission). Cette technique qui promet des augmentations importantes sur la capacité du réseau en conditions idéales, or ses vrais résultats sous le feedback limité doivent être encore décrits de manière analytique. En particulier, pour les modes d’émission connus comme JT (Joint Transmission) et CBF (Coordinated Beamforming), des expressions analytiques ont été déduites pour calculer la capacité du réseau et la probabilité de succès de transmission.Finalement une nouvelle technique de coopération de réseau pour les récepteurs avancés du type SIC (Successive Interference Cancellation) est présentée. La condition mathématique qui garantit des gains de capacité grâce à l’utilisation des récepteurs SIC est obtenue. Pour en profiter, une méthode de coopération est nécessaire pour assurer une adaptation de lien adéquate pour que l’interférence soit décodable et le débit somme soit supérieur à celui atteint avec des récepteurs traditionnels. Cette technique montre des gains importants de capacité pour des utilisateurs en bordure de cellule. / Wireless communications have become a fundamental feature of any modern society. In particular, cellular networks are essential for societal welfare but the increasing demand for data traffic set enormous scientific challenges. Increasing the network capacity is closely related to the problem of interference mitigation. In this regard, network cooperation has been studied in recent years and several different techniques have been proposed. In the first part, different transmission techniques commonly referred to as Coordinated Multi-Point Transmission (CoMP), are studied under the effect of feedback quantization and delay, unequal pathloss and other-cell interference (OCI). An analytical framework is provided, which yields closed-form expressions to calculate the ergodic throughput and outage probabilities of Coordinated Beamforming (CBF) and Joint Transmission (JT). The results indicate the optimal configuration for a system using CoMP and provide guidelines and answers to key questions, such as how many transmitters to coordinate, how many antennas to use, how many users to serve, which SNR regime is more convenient, whether to apply CBF or prefer a more complex JT, etc. Second, a new coordination technique at the receiver side is proposed to obtain sum-rate gains by means of Successive Interference Cancellation (SIC). The conditions that guarantee network capacity gains by means of SIC at the receiver are provided. To take advantage of these conditions, network coordination is needed to adapt the rates to be properly decoded at the different users involved. This technique is named Cooperative SIC and is shown to provide significant throughput gains for cell-edge users.

The cyclic prefix (CP) is usually adopted in single carrier frequency domain equalization (SC-FDE) system to avoid inter-block interference (IBI) and inter-symbol interference (ISI) in multipath fading channels. In addition, the use of CP also converts the linear convolution between the transmitted signal and the channel into a circular convolution, leading to significant decrease in receiver equalization. However, the use of CP reduces the bandwidth efficiency. Therefore the SC-FDE system without CP is investigated in this thesis. A number of schemes have been proposed to improve the performance of systems without CP, where both IBI and ICI are dramatically increased. Unfortunately, most of the existing schemes have extremely high computational complexity and are difficult to realize. In this thesis, a novel low-complexity CP reconstruction (CPR) scheme is proposed for interference cancellation, where the successive interference cancellation (SIC) and QR decomposition (QRD) are adopted. In addition, the system performance is further improved by using the fact that the interferences of different symbols are not the same. Simulation experiments are conducted to verify the system performance of the proposed scheme. It is shown that the proposed scheme can effectively reduce the interference, while maintain a low computational complexity.

In the single carrier systems with cyclic-prefix (CP), the use of CP does not only eliminate the inter-block interference (IBI), but also convert linear convolution of the transmitted signal with the channel into circular convolution, which leads to the computation complexity of the frequency domain equalization (FDE) at the receiver is reduced. Unfortunately, the use of CP considerably decreases the bandwidth utilization. In order to increase the bandwidth utilization, the single carrier systems with frequency domain equalization (SC-FDE) is investigated. When FDE is used in a single carrier system without CP, the IBI is induced by the modulated symbols and then the bit-error rate (BER) is increased. To reduce the interference and then improve the system performance, a novel interference cancellation scheme is proposed in this thesis. After FDE, it is shown that interference is induced from the right end of a time domain signal block and most of the interference is located at both ends of an equalized time domain signal block. Based on this observation, the modulated symbols which induce the interference are detected according to the maximum-likelihood (ML) principle and then the interference is regenerated and eliminated. For simplifying the computation complexity, we further propose a successive interference cancellation scheme, which is implemented by using the Viterbi algorithm. The simulation results demonstrate that the proposed scheme improves BER performance significantly in SC-FDE systems. In addition, the proposed architecture has comparable BER performance with the SC-CP systems when the multi-path channel is exponentially decayed.

Dans le domaine des réseaux satellitaires, l'apparition de terminaux interactifs à bas-prix nécessite le développement et la mise en œuvre de protocoles d'accès multiple capables de supporter différents profils d'utilisateurs. En particulier, l'Agence Spatiale Européenne (ESA) et le centre d'étude spatial allemand (DLR) ont récemment proposé des protocoles d'accès aléatoires basés sur le codage réseau couche physique et l'élimination itérative des interférences pour résoudre en partie le problème de collisions sur une voie de retour du type Slotted ALOHA. C'est dans ce contexte que s'inscrit cette thèse qui vise à fournir une amélioration dans des méthodes d'accès aléatoires existantes. Nous introduisons Multi-Slot Coded Aloha (MuSCA) comme une nouvelle généralisation of CRDSA. Au lieu de transmettre des copies du même paquet, l'émetteur envoie plusieurs parties d'un mot de code d'un code correcteur d'erreurs ; chaque partie étant précédée d'un entête permettant de localiser les autres parties du mot de code. Au niveau du récepteur, toutes les parties envoyées par le même utilisateur, y compris celles qui sont interférées par d'autres signaux, participent au décodage. Le signal décodé est ensuite soustrait du signal total. Ainsi, l'interférence globale est réduite et les signaux restant ont plus de chances d'être décodés. Plusieurs méthodes d'analyse de performance basées sur des concepts théoriques (calcul de capacité, évolution des densités) et sur des simulations sont proposées. Les résultats obtenus montrent un gain très significatif de débit global comparé aux méthodes d'accès existantes. Ce gain peut encore être augmenté en variant le taux de découpe des mots de code. En modifiant certains de ces concepts, nous proposons également une application du codage réseau couche physique basée sur la superposition de modulations pour l'accès déterministe à la voie retour des communications par satellite. Une amélioration du débit est aussi obtenue par rapport à des stratégies plus classiques de multiplexage temporal. / In the domain of satellite networks, the emergence of low-cost interactive terminals motivates the need to develop and implement multiple access protocols able to support different user profiles. In particular, the European Space Agency (ESA) and the German Aerospace Center (DLR) have recently proposed random access protocols such as Contention Resolution Diversity Coded ALOHA (CRDSA) and Irregular Repetition Slotted ALOHA (IRSA). These methods are based on physical-layer network coding and successive interference cancellation in order to attempt to solve the collisions problem on a return channel of type Slotted ALOHA.This thesis aims to provide improvements of existing random access methods. We introduce Multi-Slot Coded Aloha (MuSCA) as a new generalization of CRDSA. Instead of transmitting copies of the same packet, the transmitter sends several parts of a codeword of an error-correcting code ; each part is preceded by a header allowing to locate the other parts of the codeword. At the receiver side, all parts transmitted by the same user, including those are interfered by other signals, are involved in the decoding. The decoded signal is then subtracted from the total signal. Thus, the overall interference is reduced and the remaining signals are more likely to be decoded. Several methods of performance analysis based on theoretical concepts (capacity computation, density evolution) and simulations are proposed. The results obtained show a significant gain in terms of throughput compared to existing access methods. This gain can be even more increased by varying the codewords stamping rate. Following these concepts, we also propose an application of physical-layer network coding based on the superposition modulation for a deterministic access on a return channel of satellite communications. We observe a gain in terms of throughput compared to more conventional strategies such as the time division multiplexing.

CoordenaÃÃo de AperfeiÃoamento de Pessoal de NÃvel Superior / Este trabalho apresenta estudos sobre sistemas de comunicaÃÃo cujos sinais utilizados para a transmissÃo das informaÃÃes sÃo nÃo-ortogonais, superpostos em frequÃncia, e com espaÃamento entre portadoras menor do que a taxa de sÃmbolo. As pesquisas estÃo direcionadas na obtenÃÃo de estruturas de transmissor e receptor Ãtimos e sub-Ãtimos, na modelagem e anÃlise matemÃtica dos sistemas incluindo o canal, em propostas de estratÃgias para detecÃÃo de sÃmbolo, e na avaliaÃÃo de desempenho. SÃo propostas sete estratÃgias de recepÃÃo de N sinais m-QAM nÃo-ortogonais atravÃs do canal AWGN. Dentre as estratÃgias de detecÃÃo duas sÃo Ãtimas e as outras cinco sÃo subÃtimas. As duas estruturas de receptores Ãtimos apresentados neste trabalho sÃo: o receptor de mÃxima verossimilhanÃa (ML) clÃssico e o receptor de mÃxima verossimilhanÃa com base na decomposiÃÃo de Gram-Schmidt. Os receptores sub-Ãtimos desenvolvidos neste trabalho sÃo de dois tipos: receptores com equalizaÃÃo linear e receptores com equalizaÃÃo nÃo-linear. O primeiro tipo de receptor à desenvolvido com base nos critÃrios de erro quadrÃtico mÃdio mÃnimo (MMSE) e o de forÃagem a zero (ZF). à apresentado o desenvolvimento analÃtico do projeto de cada uma das arquiteturas de receptores lineares, assim como à determinado o erro dos estimadores. Os receptores com equalizaÃÃo nÃo-linear sÃo baseados no cancelamento de interferÃncia sucessiva (SIC). Neste trabalho, à proposta uma modificaÃÃo no algoritmo do SIC original, resultando em uma nova arquitetura de equalizaÃÃo. O desempenho dos receptores propostos à avaliado em diferentes condiÃÃes de nÃmero de portadoras e de grau de superposiÃÃo espectral atravÃs de simulaÃÃo computacional. Por fim, sÃo apresentados as conlusÃes e as perspectivas futuras de pesquisa. / This work presents studies on communication systems, whose signals used for transmission of information are non-orthogonal, overlapping in frequency and carrier spacing less than the rate of symbols. The research is aimed to obtain structures of transmitter, optimal and sub-optimal receivers using modeling and mathematical analysis of systems including the channel. Furthermore, propose strategies for symbol detection and performance evaluation. Seven strategies of reception to N signals m-QAM non-orthogonal through the AWGN channel. Among the strategies of detection two are optimal and the others five are suboptimal. The two optimal receivers structures presented in this paper are: the classical receiver maximum likelihood (ML) receiver and maximum likelihood based on the Gram-Schmidt decomposition. The suboptimal receivers in this work are of two types: receivers with linear and nonlinear equalization. The first type of receiver is developed based on the criteria of minimum mean square error (MMSE) and the zero forcing (ZF). It is presented the development of analytical design of each linear receiver architectures, as well as determined the error of the estimators. The receivers with nonlinear equalization are based on successive interference cancellation (SIC). In this paper, we propose a modification to the original algorithm of SIC, resulting in a new architecture of equalization. The performance of the proposed receivers is evaluated under different number of carriers and the degree of spectral overlap using computer simulation. Finally, we present the conclusions of this work and future prospects of the research.

In our thesis work, we analyze the performance analysis of a power domain NonOrthogonal Multiple Access (NOMA) system in which the closer user acts as fullduplex relaying to forward the signal to farther user. Because Nakagami-m distribution is a generalized case including the two common fading distributions as specialcases: Rayleigh distribution (m=1), Rician distribution (m>1). We assume that thesystem experiences Nakagami-m fading. Then, we have to analyze outage probabilityof NOMA system. Numerical results are provided for outage probability to show theeffect of system parameters on the performance of the NOMA system in full duplexrelaying over Nakagami-m fading.