Improving spectral-utilization is a core focus to cater the ever-increasing demand in data rate and system capacity required for the development of 5G. This dissertation focuses on three spectrum-reuse technologies that are envisioned to play an important role in 5G networks: device-to-device (D2D), full-duplex (FD), and nonorthogonal multiple access (NOMA). D2D allows proximal user-equipments (UEs) to bypass the cellular base-station and communicate with their intended receiver directly. In underlay D2D, the D2D UEs utilize the same spectral resources as the cellular UEs. FD communication allows a transmit-receive pair to transmit simultaneously on the same frequency channel. Due to the overwhelming self-interference encountered, FD was not possible until very recently courtesy of advances in transceiver design. NOMA allows multiple receivers (transmitters) to communicate with one transmitter (receiver) in one time-frequency resource-block by multiplexing in the power domain. Successive-interference cancellation is used for NOMA decoding. Each of these techniques significantly improves spectral efficiency and consequently data rate and throughput; however, the price paid is increased interference. Since each of these technologies allow multiple transmissions within a cell on a time-frequency resource-block, they result in interference within the cell (i.e., intracell interference). Additionally, due to the increased communication, they increase network interference from outside the cell under consideration as well (i.e., increased intercell interference). Real networks are becoming very dense; as a result, the impact of intercell interference coming from the entire network is significant. As such, using models that consider a single-cell/few-cell scenarios result in misleading conclusions. Hence, accurate modeling requires considering a large network. In this context, stochastic geometry is a powerful tool for analyzing random patterns of points such as those found in wireless networks. In this dissertation, stochastic geometry is used to model and analyze the different technologies that are to be deployed in 5G networks. This gives us insight into the network performance, showing us the impacts of deploying a certain technology into real 5G networks. Additionally, it allows us to propose schemes for integrating such technologies, mode-selection, parameter-selection, and resource-allocation that enhance the parameters of interest in the network such as data rate, coverage, and secure communication.

The demand for wireless communication is ceaselessly increasing in terms of the number of subscribers and services. Future generations of cellular networks are expected to allow not only humans but also machines to be immersively connected. However, the radio frequency spectrum is already fully allocated. Therefore, developing techniques to increase spectrum efficiency has become necessary. This dissertation analyzes two spectrum sharing techniques that enable efficient utilization of the available radio resources in cellular networks. The first technique, called full-duplex (FD) communication, uses the same spectrum to transmit and receive simultaneously. Using stochastic geometry tools, we derive a closed-form expression of an upper-bound for the maximum achievable uplink ergodic rate in FD cellular networks. We show that the uplink transmission is vulnerable to the new interference introduced by FD communications (interference from the downlink transmission in other cells), especially when the disparity in transmission power between the uplink and downlink is considerable. We further show that adjusting the uplink transmission power according to the interference power level and the channel gain can improve the uplink performance in full-duplex cellular networks. Moreover, we propose an interference management technique that allows a flexible overlap between the spectra occupied by the downlink and uplink transmissions. The flexible overlap is optimized along with the user-to-base station association, the power allocation and the channel allocation in order to maximize a network-wide utility function. The second spectrum sharing technique, called non-orthogonal multiple access (NOMA), allows a transmitter to communicate with multiple receivers through the same frequency-time resource unit. We analyze the implementation of such a scheme in the downlink of cellular networks, more precisely, in the downlink of fog radio access networks (FogRANs). FogRAN is a network architecture that takes full advantage of the edge devices capability to process and store data. We propose managing the interference for NOMA-based FogRAN to improve the network performance by jointly optimizing user scheduling, the power allocated to each resource block and the division of power between the multiplexed users. The simulation results show that significant performance gains can be achieved through proper resource allocation with both studied spectrum sharing techniques.

This dissertation presents several novel approaches to enhance security, and increase the throughput, and decrease the delay synchronization in 5G networks. First, a new physical layer paradigm was proposed for secure key exchange between the legitimate communication parties in the presence of a passive eavesdropper was presented. The proposed method ensures secrecy via pre-equalization and guarantees reliable communications using Low-Density Parity Check (LDPC) codes. One of the main findings of this research is to demonstrate through simulations that the diversity order of the eavesdropper will be zero unless the main and eavesdropping channels are almost correlated, while the probability of a key mismatch between the legitimate transmitter and receiver will be low. Simulation results demonstrate that the proposed approach achieves very low secret key mismatch between the legitimate users while ensuring very high error probability at the eavesdropper. Next, a novel medium access control (MAC) protocol Slotted Aloha-NOMA (SAN), directed to Machine to Machine (M2M) communication applications in the 5G Internet of Things (IoT) networks was proposed. SAN is matched to the low-complexity implementation and sporadic traffic requirements of M2M applications. Substantial throughput gains are achieved by enhancing Slotted Aloha with non-orthogonal multiple access (NOMA) and a Successive Interference Cancellation (SIC) receiver that can simultaneously detect multiple transmitted signals using power domain multiplexing. The gateway SAN receiver adaptively learns the number of active devices using a form of multi-hypothesis testing and a novel procedure enables the transmitters to independently select distinct power levels. Simulation results show that the throughput of SAN exceeds that of conventional Slotted Aloha by 80% and that of CSMA/CA by 20% with a probability of transmission of 0.03, with a slightly increased average delay owing to the novel power level selection mechanism. Finally, beam sweeping pattern prediction, based on the dynamic distribution of user traffic, using a form of recurrent neural networks (RNNs) called Gated Recurrent Unit (GRU) is proposed. The spatial distribution of users is inferred from data in call detail records (CDRs) of the cellular network. Results show that the user's spatial distribution and their approximate location (direction) can be accurately predicted based on CDRs data using GRU, which is then used to calculate the sweeping pattern in the angular domain during cell search. Furthermore, the data-driven proposed beam sweeping pattern prediction was compared to random starting point sweeping (RSP) to measure the synchronization delay distribution. Results demonstrate the data- drive beam sweeping pattern prediction enables the UE to initially assess the gNB in approximately 0.41 of a complete scanning cycle that is required by the RSP scheme with probability 0.9 in a sparsely distributed UE scenario.

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.

This paper is persuaded to understand the physical layer security in wireless commu-nications utilizing NOMA (Non Orthogonal Multiple Access) concepts in the presence of an eavesdropper. Physical layer security maintains the confidentiality and secrecyof the system against eavesdroppers. We use the power domain in this paper, where NOMA allows many users to share resources side by side. Power allocation concern-ing channel condition is taken into consideration where user whose channel condition is weak is allocated with eminent power to directly decode the signal, whereas theuser with better channel condition applies successive interference cancellation (SIC)to decode the signal. Here, the base station communicates with the users and sends data signals while the eavesdropper secretly eavesdrops on the confidential informa-tion simultaneously. In this thesis, to improve the physical layer security, jamming method was usedwhere users are assumed to be in full duplex, send jamming signals to degrade the performance of the eavesdropper. Analytic expressions of CDF, PDF, outage proba-bility and secrecy capacity are obtained from analyzing the NOMA jamming scheme. The numerical results are evaluated with the simulations results and analysed theeffect of jamming on improving the performance of the NOMA system in presenceof an eavesdropper.

Wireless technology has revolutionized the way people communicate. From first generation, or 1G, in the 1980s to current, largely deployed 4G in the 2010s, we have witnessed not only a technological leap, but also the reformation of associated applications. It is expected that 5G will become commercially available in 2020. 5G is driven by ever-increasing demands for high mobile traffic, low transmission delay, and massive numbers of connected devices. Today, with the popularity of smart phones, intelligent appliances, autonomous cars, and tablets, communication demands are higher than ever, especially when it comes to low-cost and easy-access solutions. Existing communication architecture cannot fulfill 5G’s needs. For example, 5G requires connection speeds up to 1,000 times faster than current technology can provide. Also, from transmitter side to receiver side, 5G delays should be less than 1ms, while 4G targets a 5ms delay speed. To meet these requirements, 5G will apply several disruptive techniques. We focus on two of them: new radio and new scheme. As for the former, we study the non-orthogonal multiple access (NOMA) and as for the latter, we use mobile edge computing (MEC). Traditional communication systems allow users to communicate alternatively, which clearly avoids inter-user interference, but also caps the connection speed. NOMA, on the other hand, allows multiple users to transmit simultaneously. While NOMA will inevitably cause excessive interference, we prove such interference can be mitigated by an advanced receiver side technique. NOMA has existed on the research frontier since 2013. Since that time, both academics and industry professionals have extensively studied its performance. In this dissertation, our contribution is to incorporate NOMA with several potential schemes, such as relay, IoT, and cognitive radio networks. Furthermore, we reviewed various limitations on NOMA and proposed a more practical model. In the second part, MEC is considered. MEC is a transformation from the previous cloud computing system. In particular, MEC leverages powerful devices nearby and instead of sending information to distant cloud servers, the transmission occurs in closer range, which can effectively reduce communication delay. In this work, we have proposed a new evaluation metric for MEC which can more effectively leverage the trade-off between the amount of computation and the energy consumed thereby. A practical communication system for wearable devices is proposed in the last part, which combines all the techniques discussed above. The challenges for wearable communication are inherent in its diverse needs, as some devices may require low speed but high reliability (factory sensors), while others may need low delay (medical devices). We have addressed these challenges and validated our findings through simulations.

With the advancement of wireless communication systems, the demand for higher data rates is increasing exponentially. Non Orthogonal Multiple Access (NOMA) is expected to play an important role in 5G new radio networks. In contrast to conventional multiple access schemes, NOMA allows different users to efficiently share the same resources (i.e., time, frequency and code) at different power levels so that the user with lower channel gain is served with a higher power and vice versa. Multiple Input Multiple Output (MIMO) technology to support multiple users, employ tens or even hundreds of antennas at the base station which increases throughput and spectrum efficiency. The combination of NOMA and MIMO techniques can achieve significant performance gains and provide better wireless services to cope with the demands of massive connectivity. In this thesis, we analyze the performance of NOMA-MIMO system. We derive analytical expressions for the performance metrics like Outage Probability (OP) and Symbol Error Rate (SER) in power domain of NOMA-MIMO communication system. The numerical results are validated with the simulation results in MATLAB and the influencing factors for better performance of the system are analysed.

Noma is a neglected non-contagious disease of the face and mouth affecting children living in extreme poverty. Due to the quick spread of the disease, the mortality rate is estimated at 90% when treatment is not started within two weeks of onset. Even though Hilfsaktion Noma e.V. (HAN) has been actively spreading awareness about the disease and offering treatment and reconstructive surgery, the mortality rate has not decreased. Moreover, patients reaching the noma centre often present severe sequela, affecting their speech, eating and drinking ability. Therefore, this study investigates the challenges faced by noma patients to seek medical care in Niger and how to overcome them. A mixed-method approach was performed; a survey among healthcare workers of HAN was supplemented with an interview with a key informant of the organisation in order to get a wider understanding of the possible challenges noma patients encounter. Accessibility to healthcare, as well as distance to the hospital and lack of transportation means were identified as the challenges with the highest impact on the health-seeking behaviour of noma patients. The lack of knowledge about noma and treatment costs were the second main challenge. This information gap is reflected in stigmatization, inadequate health care staff and seeking aid from traditional healers, which seriously endangers the life of patients. To overcome these challenges, a community-based surveillance system in combination with a multisectoral approach was proposed. This low-cost system can not only eliminate noma by facilitating the early detection of noma patients, but it can also contribute to sustainable health in Niger and other countries in the Noma belt.

Made available in DSpace on 2016-04-26T20:20:51Z (GMT). No. of bitstreams: 1 Silvia Regina Zomer.pdf: 754912 bytes, checksum: fae9f70da8d1d7f84d47a1f23e346cc3 (MD5) Previous issue date: 2012-05-15 / Whereas knowledge is conditioned by the environment that informs it, the object of this study the analysis of standard tax incidence is done in the context of Positive Law, considered as the set of valid legal norms (positive) of a society, whose values had as a background it intends, at any given time and place. Part of the observation of the legal system, under the bias of the Tax Law, as a dynamic system, structured by hierarchically organized regulatory units and through the roads of incidence, of the general rules abstraction to the concreteness of the individual norms, seeks to understand how is the assessment rule, using the hermeneuticanalytical method, based on the assumptions of the logical-semantic constructivism, as a scientific method to approach the Legal system. Finally, we analyze the constitution of the assessment rule as required by the system, considering the semiotic planes, namely the syntactic, the semantic and pragmatic, as a means of interpretation and recognition of formal and material "failures" in its development / Considerando que o conhecimento está condicionado pelo meio envolvente que o informa, o objeto deste estudo a análise da norma de incidência tributária realiza-se no contexto do Direito Positivo, assim considerado o conjunto de normas jurídicas válidas (positivadas) de uma sociedade, tendo como pano de fundo os valores por ela pretendidos, em determinado tempo e lugar. Parte da observação do ordenamento jurídico, sob o viés do Direito Tributário, como um sistema dinâmico, estruturado por unidades normativas hierarquicamente organizadas e percorrendo os caminhos da incidência, da abstração das normas gerais à concretude das normas individuais, busca entender como se dá a constituição da norma de lançamento, utilizando o método analítico-hermenêutico, alicerçado nas premissas do construtivismo lógico-semântico, como um método científico de aproximação do sistema Jurídico. Ao final, se analisa a constituição da norma do segundo as exigências do sistema, considerando os planos semióticos, a saber: o sintático, o semântico e o pragmático, como forma de interpretação e reconhecimento das falhas formais e materiais na sua elaboração

Future wireless networks will have applications that require many devices to be connected to the network. Non-orthogonal multiple access (NOMA) is a promising multiple access scheme that allows more users to simultaneously transmit in a common channel than orthogonal signaling techniques. This overloading allows for high spectral efficiencies which can support the high demand for wireless access. One notable NOMA scheme is low-density spreading (LDS), which is a code domain multiple access scheme. Low density spreading operates like code division multiple access (CDMA) in the sense that users use a spreading sequence to spread their data, but the spreading sequences have a low number of nonzero chips, hence the term low-density. The message passing algorithm (MPA) is typically used for multi-user detection (MUD) of LDS systems. The MPA detector has complexity that is exponential to the number of users contributing to each chip. LDS systems suffer from two inherent problems: high computational complexity, and vulnerability to multipath channels. In this thesis, these two problems are addressed. A lower complexity MUD technique is presented, which offers complexity that is proportional to the number of users squared. The proposed detector is based on minimum mean square error (MMSE) and parallel interference cancellation (PIC) detectors. Simulation results show the proposed MUD technique achieves reductions in multiplications and additions by 81.84% and 67.87% with a loss of about 0.25 dB with overloading at 150%. In addition, a precoding scheme designed to mitigate the effects of the multipath channel is also presented. This precoding scheme applies an inverse channel response to the input signal before transmission. This allows for the received signal to eliminate the multipath effects that destroy the low-density structure.