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

Traffic-Driven Energy Efficient Operational Mechanisms in Cellular Access Networks

Recent explosive growth in mobile data traffic is increasing energy consumption in cellular networks at an incredible rate. Moreover, as a direct result of the conventional static network provisioning approach, a significant amount of electrical energy is being wasted in the existing networks. Therefore, in recent time, the issue of designing energy efficient cellular networks has drawn significant attention, which is also the foremost motivation behind this research. The proposed research is particularly focused on the design of self-organizing type traffic-sensitive dynamic network reconfiguring mechanisms for energy efficiency in cellular systems. Under the proposed techniques, radio access networks (RANs) are adaptively reconfigured using less equipment leading to reduced energy utilization. Several energy efficient cellular network frameworks by employing inter-base station (BS) cooperation in RANs are proposed. Under these frameworks, based on the instantaneous traffic demand, BSs are dynamically switched between active and sleep modes by redistributing traffic among them and thus, energy savings is achieved. The focus is then extended to exploiting the availability of multiple cellular networks for extracting energy savings through inter-RAN cooperation. Mathematical models for both of these single-RAN and multi-RAN cooperation mechanisms are also formulated. An alternative energy saving technique using dynamic sectorization (DS) under which some of the sectors in the underutilized BSs are turned into sleep mode is also proposed. Algorithms for both the distributed and the centralized implementations are developed. Finally, a two-dimensional energy efficient network provisioning mechanism is proposed by jointly applying both the DS and the dynamic BS switching. Extensive simulations are carried out, which demonstrate the capability of the proposed mechanisms in substantially enhancing the energy efficiency of cellular networks

Advanced Technologies for Device-to-device Communications Underlaying Cellular Networks

The past few years have seen a major change in cellular networks, as explosive growth in data demands requires more and more network capacity and backhaul capability. New wireless technologies have been proposed to tackle these challenges. One of the emerging technologies is device-to-device (D2D) communications. It enables two cellular user equip- ment (UEs) in proximity to communicate with each other directly reusing cellular radio resources. In this case, D2D is able to of oad data traf c from central base stations (BSs) and signi cantly improve the spectrum ef ciency of a cellular network, and thus is one of the key technologies for the next generation cellular systems. Radio resource management (RRM) for D2D communications and how to effectively exploit the potential bene ts of D2D are two paramount challenges to D2D communications underlaying cellular networks. In this thesis, we focus on four problems related to these two challenges. In Chapter 2, we utilise the mixed integer non-linear programming (MINLP) to model and solve the RRM optimisation problems for D2D communications. Firstly we consider the RRM optimisation problem for D2D communications underlaying the single carrier frequency division multiple access (SC-FDMA) system and devise a heuristic sub- optimal solution to it. Then we propose an optimised RRM mechanism for multi-hop D2D communications with network coding (NC). NC has been proven as an ef cient technique to improve the throughput of ad-hoc networks and thus we apply it to multi-hop D2D communications. We devise an optimal solution to the RRM optimisation problem for multi-hop D2D communications with NC. In Chapter 3, we investigate how the location of the D2D transmitter in a cell may affect the RRM mechanism and the performance of D2D communications. We propose two optimised location-based RRM mechanisms for D2D, which maximise the throughput and the energy ef ciency of D2D, respectively. We show that, by considering the location information of the D2D transmitter, the MINLP problem of RRM for D2D communications can be transformed into a convex optimisation problem, which can be ef ciently solved by the method of Lagrangian multipliers. In Chapter 4, we propose a D2D-based P2P le sharing system, which is called Iunius. The Iunius system features: 1) a wireless P2P protocol based on Bittorrent protocol in the application layer; 2) a simple centralised routing mechanism for multi-hop D2D communications; 3) an interference cancellation technique for conventional cellular (CC) uplink communications; and 4) a radio resource management scheme to mitigate the interference between CC and D2D communications that share the cellular uplink radio resources while maximising the throughput of D2D communications. We show that with the properly designed application layer protocol and the optimised RRM for D2D communications, Iunius can signi cantly improve the quality of experience (QoE) of users and of oad local traf c from the base station. In Chapter 5, we combine LTE-unlicensed with D2D communications. We utilise LTE-unlicensed to enable the operation of D2D in unlicensed bands. We show that not only can this improve the throughput of D2D communications, but also allow D2D to work in the cell central area, which normally regarded as a “forbidden area” for D2D in existing works. We achieve these results mainly through numerical optimisation and simulations. We utilise a wide range of numerical optimisation theories in our works. Instead of utilising the general numerical optimisation algorithms to solve the optimisation problems, we modify them to be suitable for the speci c problems, thereby reducing the computational complexity. Finally, we evaluate our proposed algorithms and systems through sophisticated numer- ical simulations. We have developed a complete system-level simulation framework for D2D communications and we open-source it in Github: https://github.com/mathwuyue/py- wireless-sys-sim

Scalable base station switching framework for green cellular networks

With the recent unprecedented growth in the wireless market, network operators are obliged not only to find new techniques including dense deployment of base stations (BSs) in order to support high data rate services and high user density, but also to reduce the operating costs and energy consumption of various network elements. To solve these challenges, powering down certain BSs during low-traffic periods, so-called BS sleeping, has emerged as an effective green communications paradigm. While BS sleeping offers the potential to significantly lower energy consumption, it also raises many challenges, since when a BS is switched off, this can lead to, for example, coverage holes, sudden degradation in quality of service (QoS), higher transmit power dissipation in off-cell mobile stations (MSs), an inability to rapidly power up/down equipment and finally, a failure to uphold regulatory requirements. In order to realise greener network designs which both maximise energy savings whilst guaranteeing QoS, innovative BS switching mechanisms need to be developed. This thesis presents a novel BS switching framework which improves energy efficiency (EE) in comparison with existing approaches, while guaranteeing the minimum QoS and seamless services. The major technical contributions in this framework are: i) a new BS to relay station (RS) switching model where certain BSs are switched to RS mode rather than being turned off, firstly using a fixed threshold based switching algorithm utilizing temporal traffic diversity, and ii) then subsequently by means of an adaptive threshold by exploiting the inherently asymmetric traffic profile between cells, i.e., by exploiting both the temporal and spatial traffic diversity; iii) a traffic-and-interference-aware BS switching strategy that considers the impact of inter-cell interference in the decision making process to dynamically determine the best BS set to be kept active for improved EE; and finally iv) a novel scalable multimode BS switching model which enables each BS to operate in different power modes i.e., macro/micro/sleep to explore energy savings potential even at higher traffic conditions. The thesis findings conclusively confirm this new BS switching framework provides significant EE improvements from both BS and MS perspectives, under diverse network conditions and represents a notable step towards greener communications