Medium access in cognitive radio networks: From single hop to multiple hops

If channel assembling is enabled, this technique can be utilized for potential performance improvement in CRNs. Two use cases are envisaged for channel assembling. In the first use case, the system can accommodate parallel SU services in multiple channels, while in the second use case, the system allows only one SU service at a time. In the use case where parallel SU services are allowed, various channel assembling strategies are proposed and modeled in order to investigate their performance and to acquire better comprehension of the behavior of CRNs with channel assembling. Moreover, the capacity upper bound for CRNs with channel assembling in the quasistationary regime is derived. In the use case when there is only one SU service that can utilize the vacant channels at a time, we formulate channel access into two optimization problems on power allocation in multi-channel CRNs and propose various algorithms to solve these problems

MAC protocols with wake-up radio for wireless sensor networks: A review

The use of a low-power wake-up radio in wireless sensor networks is considered in this paper, where relevant medium access control solutions are studied. A variety of asynchronous wake-up MAC protocols have been proposed in the literature, which take advantage of integrating a second radio to the main one for waking it up. However, a complete and a comprehensive survey particularly on these protocols is missing in the literature. This paper aims at filling this gap, proposing a relevant taxonomy, and providing deep analysis and discussions. From both perspectives of energy efficiency and latency reduction, as well as their operation principles, state-of-the-art wake-up MAC protocols are grouped into three main categories: (1) duty cycled wake-up MAC protocols; (2) non-cycled wake-up protocols; and (3) path reservation wake-up protocols. The first category includes two subcategories: (1) static wake-up protocols versus (2) traffic adaptive wake-up protocols. Non-cycled wake-up MAC protocols are again divided into two classes: (1) always-on wake-up protocol and (2) radio-triggered wake-up protocols. The latter is in turn split into two subclasses: (1) passive wake-up MAC protocols versus (2) ultra low power active wake-up MAC protocols. Two schemes could be identified for the last category, (1) broadcast based wake-up versus (2) addressing based wake-up. All these classes are discussed and analyzed in this paper, and canonical protocols are investigated following the proposed taxonomy

Facilitating Flexible Link Layer Protocols for Future Wireless Communication Systems

This dissertation addresses the problem of designing link layer protocols which are flexible enough to accommodate the demands offuture wireless communication systems (FWCS).We show that entire link layer protocols with diverse requirements and responsibilities can be composed out of reconfigurable and reusable components.We demonstrate this by designing and implementinga novel concept termed Flexible Link Layer (FLL) architecture.Through extensive simulations and practical experiments, we evaluate a prototype of the suggested architecture in both fixed-spectrumand dynamic spectrum access (DSA) networks. FWCS are expected to overcome diverse challenges including the continual growthin traffic volume and number of connected devices.Furthermore, they are envisioned to support a widerange of new application requirements and operating conditions.Technology trends, including smart homes, communicating machines, and vehicularnetworks, will not only grow on a scale that once was unimaginable, they will also become the predominant communication paradigm, eventually surpassing today's human-produced network traffic. In order for this to become reality, today's systems have to evolve in many ways.They have to exploit allocated resources in a more efficient and energy-conscious manner.In addition to that, new methods for spectrum access and resource sharingneed to be deployed.Having the diversification of applications and network conditions in mind, flexibility at all layers of a communication system is of paramount importance in order to meet the desired goals. However, traditional communication systems are often designed with specific and distinct applications in mind. Therefore, system designers can tailor communication systems according to fixedrequirements and operating conditions, often resulting in highly optimized but inflexible systems.Among the core problems of such design is the mix of data transfer and management aspects.Such a combination of concerns clearly hinders the reuse and extension of existing protocols. To overcome this problem, the key idea explored in this dissertation is a component-based design to facilitate the development of more flexible and versatile link layer protocols.Specifically, the FLL architecture, suggested in this dissertation, employs a generic, reconfigurable data transfer protocol around which one or more complementary protocols, called link layer applications, are responsible for management-related aspects of the layer. To demonstrate the feasibility of the proposed approach, we have designed andimplemented a prototype of the FLL architecture on the basis ofa reconfigurable software defined radio (SDR) testbed.Employing the SDR prototype as well as computer simulations, thisdissertation describes various experiments used to examine a range of link layerprotocols for both fixed-spectrum and DSA networks. This dissertation firstly outlines the challenges faced by FWCSand describes DSA as a possible technology component for their construction.It then specifies the requirements for future DSA systemsthat provide the basis for our further considerations.We then review the background on link layer protocols, surveyrelated work on the construction of flexible protocol frameworks,and compare a range of actual link layer protocols and algorithms.Based on the results of this analysis, we design, implement, and evaluatethe FLL architecture and a selection of actual link layer protocols. We believe the findings of this dissertation add substantively to the existing literature on link layer protocol design and are valuable for theoreticians and experimentalists alike

Experimental study of cognitive radio test-bed using USRP

Cognitive Radio is an emerging technology that enables efficient utilization of the spectrum. As such, it has created great interests in industrial and research fields. Many people have proposed test-bed models for the performance analysis of primary and secondary users in a real-time noise environment. However, these test-beds are generally lacking in their range of capabilities as well as accurate implementation of the proposed models. In this thesis, we develop our test-bed on USRP to achieve the spectrum sensing and co-existence of primary and secondary users, while implementing the rendezvous protocols for secondary traffic coordination. We first demonstrate the spectrum sensing on the primary users using an energy detector(Average periodogram analysis) to obtain the average power of the primary channel under two different channel conditions (busy or idle). The focus is extended on developing the Markov traffic model and the Coded OFDM transceivers, while discussing the practical limitations for Markov traffic and viable solutions for reducing the burst errors for Coded OFDM. Finally, a four-node test-bed model of primary and secondary users is analyzed with the interference metrics (packet loss and error rate) for different scenarios. Also, the throughput and the interference metrics are compared for different rendezvous protocols of the secondary users

Link Scheduling Algorithms For In-Band Full-Duplex Wireless Networks

In the last two decades, wireless networks and their corresponding data traffic have grown significantly. This is because wireless networks have become an indispens- able and critical communication infrastructure in a modern society. An on-going challenge in communication systems is meeting the continuous increase in traffic de- mands. This is driven by the proliferation of electronic devices such as smartphones with a WiFi interface along with their bandwidth intensive applications. Moreover, in the near future, sensor devices that form the Internet of Things (IoTs) ecosystem will also add to future traffic growth. One promising approach to meet growing traffic demands is to equip nodes with an In-band-Full-Duplex (IBFD) radio. This radio thus allows nodes to transmit and receive data concurrently over the same frequency band. Another approach to in- crease network or link capacity is to exploit the benefits of Multiple-Input-Multiple- Output (MIMO) technologies; namely, (i) spatial diversity gain, which improves Signal-to-Noise Ratio (SNR) and thus has a direct impact on the data rate used by nodes, and (ii) spatial multiplexing gain, whereby nodes are able to form concurrent links to neighbors

Cognitive radio adaptive rendezvous protocols to establish network services for a disaster response

Disasters are catastrophic events that cause great damage or loss of life. In disasters, communication services might be disrupted due to damage to the existing network infrastructure. Temporary systems are required for victims and first responders, but installing them requires information about the radio environment and available spectrum. A cognitive radio (CR) can be used to provide a flexible and rapidly deployable temporary system due to its sensing, learning and decision-making capabilities. This thesis initially examines the potential of CR technology for disaster response networks (DRN) and shows that they are ideally suited to fulfill the requirements of a DRN. A software defined radio based prototype for multiple base transceiver stations based cellular network is proposed and developed. It is demonstrated that system can support a large number of simultaneous calls with sufficient call quality, but only when the background interference is low. It is concluded that to provide call quality with acceptable latency and packet losses, the spectrum should be used dynamically for backhaul connectivity. The deployment challenges for such a system in a disaster include the discovery of the available spectrum, existing networks, and neighbours. Furthermore, to set up a network and to establish network services, initially CR nodes are required to establish a rendezvous. However, this can be challenging due to unknown spectrum information, primary radio (PR) activity, nodes, and topology. The existing rendezvous strategies do not fulfill the DRN requirements and their time to rendezvous (TTR) is long. Therefore, we propose an extended modular clock algorithm (EMCA) which is a multiuser blind rendezvous protocol, considers the DRN requirements and has short TTR. For unknown nodes and topologies, a general framework for self-organizing multihop cooperative fully blind rendezvous protocol is also proposed, which works in different phases, can terminate when sufficient nodes are discovered, and is capable of disseminating the information of nodes which enter or leave a network. A synchronization mechanism is presented for periodic update of rendezvous information. An information exchange mechanism is also proposed which expedites the rendezvous process. In both single and multihop networks, EMCA provides up to 80% improvement in terms of TTR over the existing blind rendezvous strategies while considering the PR activity. A simple Random strategy, while being poorer than EMCA, is also shown to outperform existing strategies on average. To achieve adaptability in the presence of unknown PR activity, different CR operating policies are proposed which avoid the channels detected with PR activity to reduce the harmful interference, provide free channels to reduce the TTR, and can work with any rendezvous strategy. These policies are evaluated over different PR activities and shown to reduce the TTR and harmful interference significantly over the basic Listen before Talk approach. A proactive policy, which prefers to return to channels with recent lower PR activity, is shown to be best, and to improve the performance of all studied rendezvous strategies

Study and Development of Power Control Schemes within a Cognitive Radio-based Game Theoretic Framework

Projecte final de carrera fet en col.laboració amb Nokia Siemens NetworksThe requirements of the International Telecommunication Union (ITU) for the 4th generation of mobile devices raised up to 100 Mbps for high and 1Gbps for low mobility conditions. Reaching such challenging targets requires the deployment of picocells and femtocells. These techniques permit to achieve large cell capacity but also lead to di culties in terms of interference. The GRACE algorithm, based on Cognitive Radio and Game Theory, has shown a fair balance between cell capacity and outage as well as short convergence time, low complexity and easy scalability. The aim of this work is to find an e cient power control algorithm that fits GRACE these goals. Therefore, a study of Cognitive Radio, Game Theory and Power Control algorithms is developed and a new power control algorithm is proposed. The simulation results show that the Fractional Power Control can increase notably the outage performance and the energy saving to the mobile devices

Adaptação da taxa de transmissão em redes veiculares

Mestrado em Engenharia Eletrónica e TelecomunicaçõesAo longo dos últimos anos, vários progressos em comunicações sem fios têm extendido investigações a novas áreas, onde soluções baseadas em redes com fios são impraticáveis. Neste contexto apareceram as Vehicular Ad hoc NETworks (VANETs), uma classe emergente das redes Ad Hoc, para interligação e comunicação entre veículos. Devido ás suas características peculiares como alta mobilidade, topologia dinâmica, frequente perda de conectividade, as VANETs enfrentam vários desafios para definir protolocos e mecanismos fiáveis, como a adaptação da taxa de transmissão. De facto, a monitorização do tráfego das ruas através de aplicações são o núcleo das VANETs cujo desempenho depende da taxa de envio de pacotes e da taxa de sucesso que estas redes conseguem oferecer. Mecanismos de adaptação da taxa de transmissão têm como objetivo evitar a degradação do desempenho da rede devido a uma escolha muito elevada da taxa de transmissão, quando a qualidade do canal está deteorada, ou devido à utilização de uma taxa muito baixa quando as condições da qualidade do canal melhoram. Uma vez que os dispositivos que operam segundo a norma IEEE 802.11p suportam várias taxas de transmissão, é importante que estes possam adaptar a taxa de forma dinâmica de modo a obter um desempenho elevado. Assim é essencial ter um mecanismo de adaptação da taxa de transmissão que seja robusto e capaz de lidar com elevadas flutuações e assimetrias do canal, transmissões em rajada e de duração inconstante, e perda de pacotes devido ás condições do meio e à existência de terminais escondidos. Assim sendo, esta dissertação permite avaliar e comparar os mecanismos existentes para redes sem fios, em ambientes veiculares usando o Network Simulator 3 (NS-3) e o Simulator of Urban Mobility (SUMO). Depois de analisar os principais mecanismos presentes na literatura, foram selecionados quatro para serem testados: Adaptive Auto Rate Fall Back-Collision Detection (AARF-CD), Collision-Aware Rate Adaptation (CARA), Minstrel e o Ideal. Serão considerados dois tipos de cenários: auto-estrada e urbano. A comparação dos algoritmos será baseada em métricas conhecidas como a taxa de envio de pacotes, taxa de sucesso e a percentagem de retransmissões para vários níveis de transmissão. Os resultados experimentais mostraram que o AARFCD atingiu um desempenho superior, quando comparado com os restantes algoritmos. O CARA foi o segundo melhor algoritmo segundo as métricas consideradas. De realçar que o AARF-CD obteve uma taxa de sucesso superior ao do CARA, apesar deste oferecer uma taxa de envio de pacotes superior em certos cenários. Em relação ao atraso na rede, tanto o AARFCD como o CARA alcançaram resultados similares. Foi também concluído que algoritmos com diferenciação de perdas de pacotes como o AARF-CD e o CARA oferecem uma melhor adaptação da taxa de transmissão. Por fim, é sugerido um algoritmo de adatação da taxa de transmissão que tem em conta parâmetros externos, como a velocidade, distância e a densidade de veículos. Cada parâmetro é considerado de acordo com a sua influência na transmissão de dados através de pesos. Desta forma os parâmetros que afetam mais a adaptação da taxa de transmissão serão associados a pesos maiores. A adaptação da taxa de transmissão será baseada num processo de pesos, de acordo com o efeito das condições exteriores no desempenho da rede.Over the last years, several progresses in wireless communications have extended research in new sub-areas, where wired solutions are impracticable. In this context, VANETs arose as an emerging area of wireless ad hoc networks, which connect and allow communication between vehicles. Due to its peculiar characteristics such as high mobility, dynamic topology and frequent loss of connectivity, VANETs face many challenges to de ne reliable protocols and mechanisms like rate adaptation schemes. Indeed tra c querying and road sensing applications are the core of VANETs whose performance depends on the throughput and the success ratio these networks can provide. Rate adaptation mechanisms aim to avoid performance network degradation due to rate over-selection when channel quality is deteriorated or rate under-selection when channel quality improves. Since IEEE 802.11p supports multi-rate capabilities, devices must adapt their transmission rate dynamically in order to achieve a high performance. Thus it is critical to have a robust rate adaptation mechanism that can deal with high uctuation and asymmetry of channels, bursty and infrequent duration transmissions, and loss packet own to the extreme environment conditions or hidden terminals. Thereby, this dissertation evaluates and compares the existing rate adaptation mechanisms for wireless in vehicular environments, using NS-3 and SUMO. Four mechanisms: AARF-CD, CARA, Minstrel and Ideal were selected to be compared, after analysing the main mechanisms across literature. It will be considered two types of scenarios: highway and urban scenario. The comparison between the algorithms will be based on known metrics: network throughput, success ratio, delay and percentage of retransmissions. Experimentation results showed that AARF-CD achieved higher performance when compared with the remaining algorithms in both scenarios. CARA was the second best algorithm, considering the same metrics. Although CARA provides higher throughput in certain scenarios, it is outperformed by AARF-CD in terms of rate success. Regarding delay, AARF-CD and CARA attained similar results. It was also concluded that algorithms with loss di erentiation such as AARF-CD and CARA provide better rate adaptation. Finally, it is suggested a rate adaptation algorithm which considers external parameters like velocity, distance and density of nodes. Each parameter is considered according to its impact in the data transmission through weights. Parameters that a ect more the rate adaptation are associated to larger weights. Thus, the rate adaptation is based on a weighted process according to the e ect of external conditions in the network performance