Methods for Cellular Network's Operation in Unlicensed mmWave Bands

The 5G New Radio (NR) specifications by 3GPP include millimeter wave (mmWave) based operations for high data rates. To further satisfy the ever increasing demand for data rates, 5G NR can also be operated on the unlicensed mmWave bands. In this direction, various channel access schemes that consider Listen Before Talk (LBT) and Listen Before Receive (LBR) have been proposed in the literature. However, a thorough comparison of these schemes for fair coexistence with 60 GHz WiFi, also termed as WiGig, in different scenarios is needed. Hence, in this paper, we compare the performance of a combination of omni-directional and directional channel access schemes with LBTILBR/both in the presence of a realistic mmWave array antenna pattern, 3GPP mmWave Indoor path loss model, and fixed backoff mechanism for collision avoidance. Through extensive simulations, we show that the directional LBT combined with directional LBR and omni-directional LBT schemes perform better than other schemes in terms of sum rate, mean rate, and minimum rate in the system. Moreover, directional LBT performs better in terms of number of channel access and proportional fairness in the system as compared to other channel access schemes. © 2020 IEEE

Full-Duplex Cognitive Radio: A New Design Paradigm for Enhancing Spectrum Usage

With the rapid growth of demand for ever-increasing data rate, spectrum resources have become more and more scarce. As a promising technique to increase the efficiency of the spectrum utilization, cognitive radio (CR) technique has the great potential to meet such a requirement by allowing un-licensed users to coexist in licensed bands. In conventional CR systems, the spectrum sensing is performed at the beginning of each time slot before the data transmission. This unfortunately results in two major problems: 1) transmission time reduction due to sensing, and 2) sensing accuracy impairment due to data transmission. To tackle these problems, in this paper we present a new design paradigm for future CR by exploring the full-duplex (FD) techniques to achieve the simultaneous spectrum sensing and data transmission. With FD radios equipped at the secondary users (SUs), SUs can simultaneously sense and access the vacant spectrum, and thus, significantly improve sensing performances and meanwhile increase data transmission efficiency. The aim of this article is to transform the promising conceptual framework into the practical wireless network design by addressing a diverse set of challenges such as protocol design and theoretical analysis. Several application scenarios with FD enabled CR are elaborated, and key open research directions and novel algorithms in these systems are discussed

Distributed Cognitive RAT Selection in 5G Heterogeneous Networks: A Machine Learning Approach

The leading role of the HetNet (Heterogeneous Networks) strategy as the key Radio Access Network (RAN) architecture for future 5G networks poses serious challenges to the current cell selection mechanisms used in cellular networks. The max-SINR algorithm, although effective historically for performing the most essential networking function of wireless networks, is inefficient at best and obsolete at worst in 5G HetNets. The foreseen embarrassment of riches and diversified propagation characteristics of network attachment points spanning multiple Radio Access Technologies (RAT) requires novel and creative context-aware system designs. The association and routing decisions, in the context of single-RAT or multi-RAT connections, need to be optimized to efficiently exploit the benefits of the architecture. However, the high computational complexity required for multi-parametric optimization of utility functions, the difficulty of modeling and solving Markov Decision Processes, the lack of guarantees of stability of Game Theory algorithms, and the rigidness of simpler methods like Cell Range Expansion and operator policies managed by the Access Network Discovery and Selection Function (ANDSF), makes neither of these state-of-the-art approaches a favorite. This Thesis proposes a framework that relies on Machine Learning techniques at the terminal device-level for Cognitive RAT Selection. The use of cognition allows the terminal device to learn both a multi-parametric state model and effective decision policies, based on the experience of the device itself. This implies that a terminal, after observing its environment during a learning period, may formulate a system characterization and optimize its own association decisions without any external intervention. In our proposal, this is achieved through clustering of appropriately defined feature vectors for building a system state model, supervised classification to obtain the current system state, and reinforcement learning for learning good policies. This Thesis describes the above framework in detail and recommends adaptations based on the experimentation with the X-means, k-Nearest Neighbors, and Q-learning algorithms, the building blocks of the solution. The network performance of the proposed framework is evaluated in a multi-agent environment implemented in MATLAB where it is compared with alternative RAT selection mechanisms

Characterization and Modelling of Scattered Wireless Channel at 60 GHZ in an Underground Mine Gallery

RÉSUMÉ Depuis plus d’une décennie, les applications du système de communication sans fil sont exigeantes et augmentent rapidement pour fournir des services multimédias au public. De nos jours, la recherche se concentre sur la conception de communication sans fil à haute vitesse (i.e., 1 Gbps) en particulier dans des zones denses telles que des salles de conférence, des centres commerciaux,des stades et des lieux d’événements publics ouverts. Des réseaux locaux sans fil (WLAN) et des réseaux cellulaires utilisent des hauts potentiels pour réussir les haut débit de données en utilisant différentes technologies de pointe telles que la coexistence entre l’évaluation à long terme non autorisé (LTE-U) et les canaux Wi-Fi. En outre, la faisabilité d’utiliser le spectre à haute fréquence (i.e,> 6 GHz), une couche physique à 60 GHz pour les réseaux denses sont mis en évidence lorsque des liens de communication à courte distance (par exemple, <10 m) sont nécessaires aussi bien dans WLAN (i.e, WiGig) et le réseau cellulaire (i.e, 5G petite cellule). Cependant, les applications à 60 GHz se dirigent vers la communication sans fil souterraine pour une meilleure géolocalisation, les applications haute définition (HD) de streaming vidéo dans une galerie plus grande longueur (i.e,> 100 m) en raison de sa capacité de formation de faisceau et de plus grande capacité. Pour aider le concepteur du système, il est nécessaire de connaître les informations de propagation du canal sans fil diffusé puisque le plancher de la galerie, le plafond et le mur ont différentes rugosités (i.e.,> 5 mm). Cette thèse présente les résultats de la caractérisation du canal sans fil et la modélisation statistique à 60 GHz d’une mine souterraine à CANMET ayant des galeries dont la profondeur varie entre 40 m et 70 m. Depuis plus d’une décennie, les applications du système de communication sans fil sont exigeantes et augmentent rapidement pour fournir des services multimédias au public. Les résultats montrent que l’écart angulaire de la propagation par trajets multiples est inversement proportionnel à la distance entre l’émetteur et le récepteur. Un phénomène de dispersion solide est également observé dans le canal en observant l’angle de propagation des différents trajets. Des polarisations horizontales (H) et verticales (V) ont été utilisées puisque les diagrammes de rayonnement sont différents et peuvent fournir des comportements de dispersion temporelle différents. Les résultats montrent que l’antenne à polarisation verticale fournit un plus grand nombre de trajets multiples par rapport à polarisation horizontale et une valeur plus élevée de moyenne quadratique (RMS) par rapport à une horizontale. Par ailleurs, les mesures du coefficient de réflexion ont été effectuées pour étudier l’effet de dispersion de la surface rugueuse. Étant donné qu’aucun effet de regroupement sur le canal multitrajets n’a été observé, une approche de modélisation statistique a été considérée en tenant compte des différents trajets parcourus et leur amplitude. Par insertion des paramètres de hauteur de la surface de mesure, les modèles de diffusion connus ont également été analysées pour permettre la mise en oeuvre d’une approche de modélisation du canal dispersif.----------ABSTRACT More than a decade, there is a surge in demand and development of wireless communication system applications to deliver multimedia services. Nowadays the research is focused on the design of high speed (i.e., 1 Gbps) wireless system particularly in dense areas such as conference room, shopping mall, stadium and open public events. Wireless local area network (WLAN) and cellular network are making high potential approaches to fulfill high data rate by using different advanced technologies such as coexistence between Long Term Evaluation Unlicensed (LTE-U) and Wi-Fi Wireless channels. Moreover, the feasibility to use high-frequency spectrum (i.e., > 6 GHz), a physical layer research at 60 GHz for dense networks are highlighted where short-distance communication links (i.e., 100 m) due to its beamforming capability and higher capacity. To assist the system designer, it is necessary to know the scattered wireless channel propagation information since the gallery floor, ceiling and walls consist of the different magnitude of the roughness (i.e., > 5 mm). This thesis presents the results of wireless channel characterization and statistical modeling at 60 GHz where the measurements were carried out in CANMET underground mine (40 m and 70 m gallery depths). Several measurements were conducted with different antenna configurations and polarizations. Results show that angular and temporal dispersion are proportional to the mine gallery dimensions. Results also show that the angular spread of the multipath is inversely proportional to the transmitter receiver separation distance. A strong scattering phenomenon is also observed in the channel by observing multipath angle of arrivals. The use of Horizontal (H) and vertical (V) polarizations were performed due to its different radiation pattern can provide a different temporal dispersion behavior. The results show that a vertically polarized antenna provides a lower value of path loss exponent and a higher value of root mean square (RMS) delay spread compared to a horizontal one. Since no clustering effect was observed, a statistical modeling approach with the multipath arrivals and amplitudes was considered. In addition, the reflection coefficient measurements were conducted to investigate the scattering effect from the rough surface. By inserting measured surface height parameters, the known scattering models were also analyzed to have an idea to implement a modeling approach of the scattered channel

Spectrum Sharing and SAS-CBSD Interface Simulation

Spectrum Sharing technologies enables more dynamic spectrum management regulation and framework to provide capacity for the ever-increasing demand of mobile data traffic. This thesis reviewed the background and current state of the development of Spectrum Sharing approaches. TVWS, LSA and CBRS were examined in detail as the most representative solutions. The thesis compared architectural similarities and differences between LSA and CBRS. The thesis reviewed SAS-CBSD interface protocol and continued with a practical validation of SAS-CBSD interface specification. By implementing the interface in Python, interface simulation was conducted via the assistance of automation scripts. The thesis concluded that the SAS-CBSD interface is functioning as designed, noting that ESC will further extend the spectrum access dynamism. The thesis also pointed out the need to specify SAS-relevant data models for database API standardization

On three use cases of multi-connectivity paradigm in emerging wireless networks

As envisioned by global network operators, the increasing trend of data traffic demand is expected to continue with exponential growth in the coming years. To cope with this rapid increase, significant efforts from the research community, industry and even regulators have been focused towards improving two main aspects of the wireless spectrum: (i) spectrum capacity and (ii) spectral efficiency. Concerning the spectrum capacity enhancement, the multi-connectivity paradigm has been seen to be fundamentally important to solve the capacity problem in the next generation networks. Multi-connectivity is a feature that allows wireless devices to establish and maintain multiple simultaneous connections across homogeneous or heterogeneous technologies. In this thesis, we focus on identifying the core issues in applying the multi-connectivity paradigm for different use cases and propose novel solutions to address them. Specifically, this thesis studies three use cases of the multi-connectivity paradigm. First, we study the uplink/downlink decoupling problem in 4G networks. More specifically, we focus on the user association problem in the decoupling context, which is considered challenging due to the conflicting objectives of different entities (e.g., mobile users and base stations) in the system. We use a combination of matching theory and stochastic geometry to reconcile competing objectives between users in the uplink/downlink directions and also from the perspective of base stations. Second, we tackle the spectrum aggregation problem for wireless backhauling links in unlicensed opportunistic shared spectrum bands, specifically, TV White Space (TVWS) spectrum. In relation to this, we present a DIY mobile network deployment model to accelerate the roll-out of high-end mobile services in rural and developing regions. As part of this model, we highlight the importance of low-cost and high-capacity backhaul infrastructure for which TVWS spectrum can be exploited. Building on that, we conduct a thorough analytical study to identify the characteristics of TVWS in rural areas. Our study sheds light on the nature of TVWS spectrum fragmentation for the backhauling use case, which in turn poses requirements for the design of spectrum aggregation systems for TVWS backhaul. Motivated by these findings, we design and implement WhiteHaul, a flexible platform for spectrum aggregation in TVWS. Three challenges have been tackled in this work. First, TVWS spectrum is fragmented in that the spectrum is available in non-contiguous manner. To fully utilize the available spectrum, multiple radios should be enabled to work simultaneously. However, all the radios have to share only a single antenna. The key challenge is to design a system architecture that is capable of achieving different aggregation configurations while avoiding the interference. Second, the heterogeneous nature of the available spectrum (i.e., in terms of bandwidth and link characteristics) requires a design of efficient traffic distribution algorithm that takes into account these factors. Third, TVWS is unlicensed opportunistic shared spectrum. Thus, the coordination mechanism between the two nodes of backhauling link is essential to enable seamless channel switching. Third, we study the integration of multiple radio access technologies (RATs) in the context of 4G/5G networks. More specifically, we study the potential gain of enabling the Multi-RAT integration at the Packet Data Convergence Protocol (PDCP) layer compared with doing it at the transport layer. In this work, we consider ultra-reliable low-latency communication (URLLC) as one of the motivating services. This work tackles the different challenges that arise from enabling the Multi-RAT integration at the PDCP layer, including, packet reordering and traffic scheduling

IoT Networking: Path to Ubiquitous Connectivity

University of Minnesota Ph.D. dissertation. August 2019. Major: Computer Science. Advisor: Tian He. 1 computer file (PDF); xii, 105 pages.Internet of Things (IoT) is upon us with the number of IoT connected devices reach- ing 17.68 billion in the year 2016 and keeps an increasing rate of 17%. The popularity of IoT brings the prosperity and diversity of wireless technologies as one of its founda- tions. Existing wireless technologies, such as WiFi, Bluetooth, and LTE, are evolving and new technologies, such as SigFox and LoRa, are proposed to satisfy various needs under emerging application scenarios. For example, WiFi is evolving to provide higher throughput with the novel 802.11ac technology and the Bluetooth SIG has proposed the Bluetooth Low Energy (BLE) technology to support low-power applications. However, wireless technologies are victims of their own success. The vastly increasing wireless devices compete for the limited wireless spectrum and result in the performance degradation of each device. What makes it worse is that diverse wireless devices are using heterogeneous PHY and MAC layers designs which are not compliant with each other. As a result, sophisticated wireless coordination methods working well for each homogeneous technology are not applicable in the heterogeneous wireless scenario for the failure to communicate among heterogeneous devices. This dissertation aims at fundamentally solving the burden of communication in today’s heterogeneous wireless environment. Specifically, we try to build direct communication among heterogeneous wireless technologies, referred to as the cross-technology communication (CTC). It is counter-intuition and long believed impossible, but we find two opportunities in both the packet level and physical (PHY) layer to make the challenging mission possible. First, wireless devices are commonly able to do energy-sensing of wireless packets in the air. Energy sensing is capable to figure out packet-level information, such as the packet duration and timing. Based on the energy-sensing capability, we design DCTC, a CTC technology that piggybacks cross-technology messages within the timing of transmitted wireless packets. Specifically, we slightly perturb the timing of packets emitted from a wireless device to form detectable energy patterns to establish CTC. Testbed evaluation has shown that we can successfully transmit information at 760bps while keeping the delay of each packet no longer than 0.5ms under any traffic pattern. Second, in the PHY layer, high-end wireless technologies are flexible, i.e., a larger symbol set, in the modulation and demodulation. With careful choices of symbols, those wireless technologies are able to emulate and decode the PHY layer signal of a low-end one. We propose two systems BlueBee and XBee which aim at building direct com- munication between two heterogeneous IoT technologies, Bluetooth and ZigBee, with the idea of signal emulation and cross-decoding respectively. The former achieves signal emulation by carefully choosing the Bluetooth payload bits so that the output signal emulates a legitimate ZigBee packet which can be successfully demodulated by a com- modity ZigBee devices without any changes. The latter proposes a general method to support the bidirectional communication in the PHY-layer CTC by moving the complex- ity to the high-end receiver for the demodulation of signal from a low-end transmitter. Our testbed evaluation has shown that our technologies successfully boost the data rate of the state of the arts by over 10,000x times, which is approaching the ZigBee standard. This result makes CTC possible to play more roles in real-time applications, such as network coordination. In summary, this dissertation provides a new communication paradigm in a heteroge- neous wireless environment, which is to provide direct communication for heterogeneous wireless devices. Such communication is built upon two opportunities: (i) wireless de- vices are capable to sense energy in the air so that specifically designed energy patterns can transmit cross-technology information; (ii) a high-end wireless technology is more flexible and possible to emulate and demodulate the signal from a low-end technology for communication. The technologies developed in the dissertation will be the build- ing blocks for the future designs of efficient channel coordination and ubiquitous data exchange among heterogeneous wireless devices

Contributions to IEEE 802.11-based long range communications

The most essential part of the Internet of Things (IoT) infrastructure is the wireless communication system that acts as a bridge for the delivery of data and control messages between the connected things and the Internet. Since the conception of the IoT, a large number of promising applications and technologies have been developed, which will change different aspects in our daily life. However, the existing wireless technologies lack the ability to support a huge amount of data exchange from many battery-driven devices, spread over a wide area. In order to support the IoT paradigm, IEEE 802.11ah is an Internet of Things enabling technology, where the efficient management of thousands of devices is a key function. This is one of the most promising and appealing standards, which aims to bridge the gap between traditional mobile networks and the demands of the IoT. To this aim, IEEE 802.11ah provides the Restricted Access Window (RAW) mechanism, which reduces contention by enabling transmissions for small groups of stations. Optimal grouping of RAW stations requires an evaluation of many possible configurations. In this thesis, we first discuss the main PHY and MAC layer amendments proposed for IEEE 802.11ah. Furthermore, we investigate the operability of IEEE 802.11ah as a backhaul link to connect devices over possibly long distances. Additionally, we compare the aforementioned standard with previous notable IEEE 802.11 amendments (i.e. IEEE 802.11n and IEEE 802.11ac) in terms of throughput (with and without frame aggregation) by utilizing the most robust modulation schemes. The results show an improved performance of IEEE 802.11ah (in terms of power received at long range while experiencing different packet error rates) as compared to previous IEEE 802.11 standards. Additionally, we expose the capabilities of future IEEE 802.11ah in supporting different IoT applications. In addition, we provide a brief overview of the technology contenders that are competing to cover the IoT communications framework. Numerical results are presented showing how the future IEEE 802.11ah specification offers the features required by IoT communications, thus putting forward IEEE 802.11ah as a technology to cater the needs of the Internet of Things paradigm. Finally, we propose an analytical model (named e-model) that provides an evaluation of the RAW onfiguration performance, allowing a fast adaptation of RAW grouping policies, in accordance to varying channel conditions. We base the e-model in known saturation models, which we adapted to include the IEEE 802.11ah’s PHY and MAC layer modifications and to support different bit rate and packet sizes. As a proof of concept, we use the proposed model to compare the performance of different grouping strategies,showing that the e-model is a useful analysis tool in RAW-enabled scenarios. We validate the model with existing IEEE 802.11ah implementation for ns-3.La clave del concepto Internet de las cosas (IoT) es que utiliza un sistema de comunicación inalámbrica, el cual actúa como puente para la entrega de datos y mensajes de control entre las "cosas" conectadas y el Internet. Desde la concepción del IoT, se han desarrollado gran cantidad de aplicaciones y tecnologías prometedoras que cambiarán distintos aspectos de nuestra vida diaria.Sin embargo, las tecnologías de redes computacionales inalámbricas existentes carecen de la capacidad de soportar las características del IoT, como las grandes cantidades de envío y recepción de datos desde múltiples dispositivos distribuidos en un área amplia, donde los dispositivos IoT funcionan con baterías. Para respaldar el paradigma del IoT, IEEE 802.11ah, la cual es una tecnología habilitadora del Internet de las cosas, para el cual la gestión eficiente de miles de dispositivos es una función clave. IEEE 802.11ah es uno de los estándares más prometedores y atractivos, desde su concepción orientada para IoT, su objetivo principal es cerrar la brecha entre las redes móviles tradicionales y la demandada por el IoT. Con este objetivo en mente, IEEE 802.11ah incluye entre sus características especificas el mecanismo de ventana de acceso restringido (RAW, por sus siglas en ingles), el cual define un nuevo período de acceso al canal libre de contención, reduciendo la misma al permitir transmisiones para pequeños grupos de estaciones. Nótese que para obtener una agrupación óptima de estaciones RAW, se requiere una evaluación de las distintas configuraciones posibles. En esta tesis, primero discutimos las principales mejoras de las capas PHY y MAC propuestas para IEEE 802.11ah. Además, investigamos la operatividad de IEEE 802.11ah como enlace de backhaul para conectar dispositivos a distancias largas. También, comparamos el estándar antes mencionado con las notables especificaciones IEEE 802.11 anteriores (es decir, IEEE 802.11n y IEEE 802.11ac), en términos de rendimiento (incluyendo y excluyendo la agregación de tramas de datos) y utilizando los esquemas de modulación más robustos. Los resultados muestran mejores resultados en cuanto al rendimiento de IEEE 802.11ah (en términos de potencia recibida a largo alcance, mientras se experimentan diferentes tasas de error de paquetes de datos) en comparación con los estándares IEEE 802.11 anteriores.Además, exponemos las capacidades de IEEE 802.11ah para admitir diferentes aplicaciones de IoT. A su vez, proporcionamos una descripción general de los competidores tecnológicos, los cuales contienden para cubrir el marco de comunicaciones IoT. También se presentan resultados numéricos que muestran cómo la especificación IEEE 802.11ah ofrece las características requeridas por las comunicaciones IoT, presentando así a IEEE 802.11ah como una tecnología que puede satisfacer las necesidades del paradigma de Internet de las cosas.Finalmente, proponemos un modelo analítico (denominado e-model) que proporciona una evaluación del rendimiento utilizando la característica RAW con múltiples configuraciones, el cual permite una rápida adaptación de las políticas de agrupación RAW, de acuerdo con las diferentes condiciones del canal de comunicación. Basamos el e-model en modelos de saturación conocidos, que adaptamos para incluir las modificaciones de la capa MAC y PHY de IEEE 802.11ah y para poder admitir diferentes velocidades de transmisión de datos y tamaños de paquetes. Como prueba de concepto, utilizamos el modelo propuesto para comparar el desempeño de diferentes estrategias de agrupación, mostrando que el e-model es una herramienta de análisis útil en escenarios habilitados para RAW. Cabe mencionar que también validamos el modelo con la implementación IEEE 802.11ah existente para ns-3