Power allocation in a QoS-aware cellular-based vehicular communication system.

Masters Degree. University of KwaZulu- Natal, Durban.The task of a driver assistance system is to monitor the surrounding environment of a vehicle and provide an appropriate response in the case of detecting any hazardous condition. Such operation requires real-time processing of a large amount of information, which is gathered by a variety of sensors. Vehicular communication in future vehicles can pave the way for designing highly efficient and cost-effective driver assistance systems based on collaborative and remote processing solutions. The main transmission links of vehicular communication systems are vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I). In this research, a cellular-based vehicular communication system is proposed where Device-to-device (D2D) communication links are considered for establishing V2V links, and cellular communication links are employed for V2I links. D2D communication is one of the enablers of the next generation of cellular networks for improving spectrum and power utilization. D2D communication allows direct communication between user equipments within a cellular system. Nevertheless, implementing D2D communication should not defect nearby ongoing communication services. As a result, interference management is a significant aspect of designing D2D communication systems. Communication links in a cellular network are supposed to support a required level of data rates. The capacity of a communication channel is directly proportional to the energy of a transmitted signal, and in fact, achieving the desired level of Quality of Service (QoS) requires careful control of transmission power for all the radio sources within a system. Among different methods that are recommended for D2D communications, in-band D2D can offer better control over power transmission sources. In an underlay in-band D2D communication system, D2D user equipments (DUEs) usually reuse the cellular uplink (UL) spectrum. In such a system, the level of interference can effectively be managed by controlling the level of power that is transmitted by user equipments. To effectively perform the interference management, knowledge of the channel state information is required. However, as a result of the distributed nature of DUEs, such information is not fully attainable in a practical D2D system. Therefore, statistical methods are employed to find boundaries on the allocated transmission powers for achieving sufficient spectral efficiencies in V2I and V2V links without considering any prior knowledge on vehicles’ locations or the channel state information. Furthermore, the concepts of massive multiple-input multiple-output and underlay D2D communication sharing the uplink spectrum of a cellular system are used to minimize the interference effect

Device-to-device communication : effects of using spatial spectrum sensing and dual band networks

Orientador: Paulo CardieriDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de ComputaçãoResumo: A técnica comunicação Device-to-Device (D2D) é considerada como uma das tecnologias candidatas para a implementação de sistemas celulares de quinta geração (5G). Basicamente, essa técnica permite a comunicação direta entre dois terminais de usuário que estejam próximos entre si, sem, assim, usar a estação rádio base (BS, Base Station). A técnica D2D tem a capacidade de fornecer altas taxas de dados com menor consumo de energia, devido à menor distância do enlace entre transmissor e receptor. Essas características tornam-se atraentes para os pesquisadores que estão na busca de tecnologias capazes de atender o alto tráfego de dados que atualmente circula nas redes sem fio, e garantir os padrões de qualidade de serviço (QoS, Quality of Service) esperados pelos usuários. Esse presente trabalho estuda a técnica de comunicação D2D em uma rede celular no modo underlay de compartilhamento de canal, isto é, quando um canal uplink da rede celular é compartilhado entre terminais operando no modo convencional, isto é, conectados às BS, e terminais operando no modo D2D. Com essa forma de compartilhamento de canal, a interferência entre os enlaces celulares e D2D pode degradar o desempenho da rede. Para controlar o nível de interferência, assume-se que os terminais operando no modo D2D utilizam a técnica de spectrum sensing (SS) para detectar o estado do canal (livre ou ocupado), antes de iniciar a sua transmissão. São considerados nesse estudo dois cenários de uso do spectrum sensing. No Cenário I, os terminais D2D usam SS para evitar a interferência entre eles e os terminais celulares. Nesse sentido, como consequência do processo de SS, as posições dos transmissores D2D podem ser modeladas pelo processo pontual chamado Poisson Hole Process. No Cenário II, o processo de spectrum sensing empregado pelos terminais D2D é usado para detectar o uso do canal não apenas por algum terminal celular, mas também por algum terminal D2D. O processo pontual resultante que modela os transmissores D2D neste cenário é uma versão do chamado processo Matérn Point Process. Para esses dois cenários são derivadas expressões de probabilidade de outage para os enlaces celulares e enlaces D2D, empregando ferramentas de Geometria Estocástica, usando os processos pontuais mencionados. Com base nessas expressões de probabilidade de outage, é apresentada uma análise do desempenho da rede celular-D2D. Outra tecnologia atraente para sistemas 5G é a comunicação na faixa de ondas milimétricas, uma vez que tal faixa apresenta uma largura de banda maior, permitindo altas taxas de dados. No entanto, a comunicação na banda de ondas milimétricas requer linha de visada, sendo, portanto, altamente susceptível a bloqueio do enlace devido às condições de propagação. Esse trabalho estuda também a comunicação D2D em um cenário em que os terminais podem operar nas bandas de ondas milimétricas e microondas, combinado com um esquema de retransmissão de pacotes. No cenário estudado aqui, os terminais D2D operam prioritariamente na banda de ondas milimétricas, mas quando as condições de propagação nessa banda se deterioram, eles podem mudar para a banda de microondas, como uma tentativa de melhorar o desempenho geral. Também usando elementos de geometria estocástica, são derivadas expressões de probabilidade de outage para a comunicação nas duas bandas, e uma análise do desempenho desse esquema de transmissão é investigadoAbstract: Device-to-Device Communication is deemed as one of the key technologies for the fifth generation of cellular systems (5G). Basically, this strategy of communication allows user terminals to communicate directly with each other, without any assistance from base stations. Device-to-device communication is capable of providing high data rate, coverage extension, and reduced energy consumption. Due to the shorter distance of the link between transmitter and receiver. These features are attractive to researchers who are searching for technologies can handle the high data traffic that currently circulates on wireless networks, and ensures the quality of service standards (QoS), expected by users. This present work investigates the performance of an underlay D2D cellular network, in which D2D terminals and cellular terminals share the same uplink channel. In order to control the level of interference, we assume that D2D terminals employ spectrum sensing (SS) in order to detect the presence of other transmission on the target channel. Two scenarios are considered regarding the use of spectrum sensing. In Scenario I, the D2D terminals employ SS to avoid interference between them and cellular terminals. Therefore, the locations of D2D transmitters can be modeled by a Poisson Hole Process. In Scenario II, spectrum sensing is used to control the interference among D2D terminals and cellular terminals, as in Scenario I, and the interference among D2D terminals. In this scenario, the locations of D2D terminals are better modeled by a version of the Matérn Point Process. Using elements of Stochastic Geometry, expressions for outage probabilities in both scenarios are derived and used in the performance analysis of these two scenarios. Another attractive technology for 5G cellular systems is millimeter-wave communication, due to the availability of large bandwidth at this frequency band, allowing for a high data rate. However, the communication in the millimeter wave band is highly susceptible to link blockage, degrading the communication performance. In this work, we investigate the performance of a D2D network in which terminals can operate either in the millimeter-wave band or in the microwave band, combined with a packet retransmission scheme and beam-forming. The terminals primarily operate in the millimeter-wave band, and when the propagation conditions deteriorate, they can switch to the microwave band as an attempt to improve the overall performance. Using tools from Stochastic Geometry, the performance of this communication strategy is investigatedMestradoTelecomunicações e TelemáticaMestra em Engenharia ElétricaCAPE

Power control for predictable communication reliability in wireless cyber-physical systems

Wireless networks are being applied in various cyber-physical systems and posed to support mission-critical cyber-physical systems applications. When those applications require reliable and low-latency wireless communication, ensuring predictable per-packet communication reliability is a basis. Due to co-channel interference and wireless channel dynamics (e.g. multi-path fading), however, wireless communication is inherently dynamic and subject to complex uncertainties. Power control and MAC-layer scheduling are two enablers. In this dissertation, cross-layer optimization of joint power control and scheduling for ensuring predictable reliability has been studied. With an emphasis on distributed approaches, we propose a general framework and additionally a distributed algorithm in static networks to address small channel variations and satisfy the requirements on receiver-side signal-to-interference-plus-noise-ratio (SINR). Moreover, toward addressing reliability in the settings of large-scale channel dynamics, we conduct an analysis of the strategy of joint scheduling and power control and demonstrate the challenges. First, a general framework for distributed power control is considered. Given a set of links subject to co-channel interference and channel dynamics, the goal is to adjust each link\u27s transmission power on-the-fly so that all the links\u27 instantaneous packet delivery ratio requirements can be satised. By adopting the SINR high-delity model, this problem can be formulated as a Linear Programming problem. Furthermore, Perron-Frobenius theory indicates the characteristic of infeasibility, which means that not all links can nd a transmission power to meet all the SINR requirements. This nding provides a theoretical foundation for the Physical-Ratio-K (PRK) model. We build our framework based on the PRK model and NAMA scheduling. In the proposed framework, we dene the optimal K as a measurement for feasibility. Transmission power and scheduling will be adjusted by K and achieve near-optimal performance in terms of reliability and concurrency. Second, we propose a distributed power control and scheduling algorithm for mission-critical Internet-of-Things (IoT) communications. Existing solutions are mostly based on heuristic algorithms or asymptotic analysis of network performance, and there lack eld-deployable algorithms for ensuring predictable communication reliability. When IoT systems are mostly static or low mobility, we model the wireless channel with small channel variations. For this setting, our approach adopts the framework mentioned above and employs feedback control for online K adaptation and transmission power update. At each time instant, each sender will run NAMA scheduling to determine if it can obtain channel access or not. When each sender gets the channel access and sends a packet, its receiver will measure the current SINR and calculate the scheduling K and transmission power for the next time slot according to current K, transmission power and SINR. This adaptive distributed approach has demonstrated a signicant improvement compared to state-of-the-art technique. The proposed algorithm is expected to serve as a foundation for distributed scheduling and power control as the penetration of IoT applications expands to levels at which both the network capacity and communication reliability become critical. Finally, we address the challenges of power control and scheduling in the presence of large-scale channel dynamics. Distributed approaches generally require time to converge, and this becomes a major issue in large-scale dynamics where channel may change faster than the convergence time of algorithms. We dene the cumulative interference factor as a measurement of impact of a single link\u27s interference. We examine the characteristic of the interference matrix and propose that scheduling with close-by links silent will be still an ecient way of constructing a set of links whose required reliability is feasible with proper transmission power control even in the situation of large-scale channel dynamics. Given that scheduling alone is unable to ensure predictable communication reliability while ensuring high throughput and addressing fast-varying channel dynamics, we demonstrate how power control can help improve both reliability at each time instant and throughput in the long-term. Collectively, these ndings provide insight into the cross-layer design of joint scheduling and power control for ensuring predictable per-packet reliability in the presence of wireless network dynamics and uncertainties