Current Massively Multi-player Online Games (MMOGs) have enormous server-side bandwidth requirements. The costs of providing this bandwidth is in turn passed on to the consumer in the form of high monthly subscription fees. Prior work has primarily focused on distributing this bandwidth using peer-to-peer architectures, but these architectures have difficulty preventing cheating, overwhelming low resource peers, and maintaining consistent game state. We have developed a hybrid game architecture that combines client-server and peer-to-peer technologies to prevent cheating, maintain centralized and consistent game state, significantly reduce central server bandwidth, and prevent lower capacity players from being overwhelmed. By dramatically reducing the bandwidth needed to host a game without introducing additional liabilities, our hybrid architecture reduces the costs associated with that bandwidth and allows MMOG developers to reduce the cost of monthly subscription fees. In addition, because the central server will need less bandwidth per player, a single server is able to support considerably more concurrent players. Our experiments show that bandwidth can be reduced by up to 95% and a single server can support a game twice as large.

Recent leaps in eye tracking technology have made it possible to enable eye tracking as a cheap, reliable and efficient addition to the human computer interaction technologies. This thesis looks into the possibility of utilizing it for client aware video streaming. Increasingly people are consuming high quality video content on wireless network devices, thus there is need to optimize bandwidth consumption for efficient delivery of such high resolution content, both for 2D and 360°videos.This work proposes SEEN (Smart Eye-tracking Enabled Networking), a novel approach to streaming video content using real time eye tracking information. This uses HEVC video tiling techniques to display high and low qualities in the same video frame depending on where the user is looking. The viability of proposed approach is validated using extensive user testing conducted on a Quality of Experience (QoE) testbed which was also developed as part of this thesis. Test results show significant bandwidth savings of up to 71% for 2D videos on standard 4K screens, and up to 83% for 360°videos on Virtual Reality (VR) headsets for acceptable QoE ratings. A comparative study on viewport tracking and eye tracking for VR headsets is also included in the thesis in order to further advocate the necessity of eye tracking.This research was conducted in collaboration with Ericsson, Tobii and KTH under the umbrella project SEEN: Smart Eye-tracking Enabled Networking. / Nya framsteg inom ögonstyrningsteknologi har möjliggjort att betrakta ögonstyrning (o.k.s. eyetracking) som ett billigt, pålitligt och effektivt tillägg till teknologier för människa-dator interaktion. Det här examensarbetet utforskar möjligheten att använda ögonstyrning för klientmedveten videoströmning. Allt fler personer förbrukar videoinnehåll av hög kvalitet genom trådlösa nätverk, därmed finns det ett behov av att optimera bandbreddskonsumtionen för effektiv leverans av ett sådant högkvalitativt innehåll, både för 2Doch 360°-videor.Det här arbetet introducerar SEEN (Smart Eye-tracking Enabled Networking), en ny approach för att strömma videoinnehåll, som bygger på realtidsinformation från ögonstyrning. Den använder HEVC-metoder för rutindelning av video för att visa högkvalitativt och lågkvalitativt innehåll i samma videoram, beroende på vart användaren tittar. Lönsamheten av den föreslagna approachen validerades med hjälp av omfattande användartester utförda på en testbädd för upplevelsekvalité (Quality of Experience, QoE) som också utvecklades som en del av det här examensarbetet. Testresultaten visar betydande bandbreddsbesparingar på upp till 71% för 2D-videor på vanliga 4K-skärmar samt upp till 83% för 360°-videor på VR-headset för acceptabla QoE-betyg. En komparativ studie om viewport tracking och ögonstyrning i VR-headset är också inkluderad i det här examensarbetet för att ytterligare förespråka behovet av ögonstyrning.Denna forskning genomfördes i samarbete med Ericsson, Tobii och KTH under paraplyprojektet SEEN: Smart Eye-tracking Enabled Networking.

Efficiency and transient response are two key requirements for DC-DC converters. Topology and control are two key topics in this dissertation. A variety of techniques for DC-DC converter performance improvement are presented in this work. Focusing on the efficiency issue, a variety of clamping techniques including both active and passive methods are presented after the ringing issues in DC-DC converters are investigated. By presenting the clamping techniques, a big variety of energy management concepts are introduced. The active bridge-capacitor tank clamping and FET-diode-capacitor tank clamping are close ideas, which transfer the leakage inductor energy to clamping capacitor to prevent oscillation between leakage inductor and junction capacitor of MOSFETs. The two-FET-clamping tank employs two MOSFETs to freewheeling the leakage current when the main MOSFETs of the half-bridge are both off. Driving voltage variation on the secondary side Synchronous Rectifier (SR) MOSFETs in self-driven circuit due to input voltage variation in bus converter applications is also investigated. One solution with a variety of derivations is proposed using zerner-capacitor combination to clamping the voltage while maintaining reasonable power losses. Another efficiency improvement idea comes from phase-shift concept in DC-DC converters. By employing phase-shift scheme, the primary side and the secondary side two MOSFETs have complementary driving signals respectively, which allow the MOSFET to be turned on with Zero Voltage Switching (ZVS). Simulation verified the feasibility of the proposed phase-shifted DC-DC converter. From the control scheme point of view, a novel peak current mode control concept for half-bridge topologies is presented. Aiming at compensating the imbalanced voltage due to peak current mode control in symmetric half-bridge topologies, an additional voltage compensation loop is used to bring the half-bridge capacitor voltage back to balance. In the proposed solutions, one scheme is applied on symmetric half-bridge topology and the other one is applied on Duty-cycle-shifted (DCS) half-bridge topology. Both schemes employ simple circuitry and are suitable for integration. Loop stability issues are also investigated in this work. Modeling work shows the uncompensated half-bridge topology cannot be stabilized under all conditions and the additional compensation loop helps to prevent the voltage imbalance effectively.

Yes / This paper presented a planar printed multiple-input-multiple-output (MIMO) antenna with a dimension of 100 x 45 mm2. It composed of two crescent shaped radiators placed symmetrically with respect to the ground plane. Neutralization line applied to suppress mutual coupling. The proposed antenna examined both theoretically and experimentally, which achieves an impedance bandwidth of 18.67% (over 2.04-2.46 GHz) with a reflection coefficient < -10 dB and mutual coupling minimization of < -20 dB. An evaluation of MIMO antennas is presented, with analysis of correlation coefficient, total active reflection coefficient (TARC), capacity loss and channel capacity. These characteristics indicate that the proposed antenna suitable for some wireless applications.

School of Computing, Informatics and Media / Localised QoS routing is a relatively new, alternative and viable approach to solve the problems of traditional QoS routing algorithms which use global state information resulting in the imposition of a large communication overhead and route flapping. They make use of a localised view of the network QoS state in source nodes to select paths and route flows to destination nodes. Proportional Sticky Routing (PSR) and Credit Based Routing (CBR) have been proposed as localised QoS routing schemes and these can offer comparable performances. However, since network state information for a specific path is only updated when the path is used, PSR and CBR operate with decision criteria that are often stale for paths that are used infrequently. The aim of this thesis is to focus on localised QoS routing and contribute to enhancing the scalability of QoS routing algorithms. In this thesis we have developed three new localised QoS routing schemes which are called Score Based QoS Routing (SBR), Bandwidth Based QoS Routing (BBR) and Delay Based Routing (DBR). In some of these schemes, the path setup procedure is distributed and uses the current network state to make decisions thus avoiding problems of staleness. The methods also avoid any complicated calculations. Both SBR and BBR use bandwidth as the QoS metric and mean delay is used as the QoS metric in DBR. Extensive simulations are applied to compare the performance of our proposed algorithms with CBR and the global Dijkstra¿s algorithm for different update intervals of link state, different network topologies and using different flow arrival distributions under a wide range of traffic loads. It is demonstrated by simulation that the three proposed algorithms offer a superior performance under comparable conditions to the other localised and global algorithms.

Mobile handset manufacturers have begun to include wireless LAN (WLAN) interfaces in their cellular handsets. This allows users to access WLAN networks when they are available and to revert to conventional cellular communications otherwise. In this way the handset can dynamically use the "best" available network, by switching connections between the two network interfaces. This switching is referred to as a vertical handoff (VHO). When handling real-time connections, handsets must be capable of performing a seamless vertical handoff. This occurs when the interface switching does not disrupt the quality of service requirements of the active connections. Vertical handoffs are generally time consuming, and this delay creates a difficult problem since WLAN coverage can be lost very abruptly. In this thesis, we propose and investigate several methods of mitigating this problem. A solution based on using a Vertical Handoff Support Node (VHSN) is proposed. When the WLAN link is lost, the VHSN is able to quickly redirect packets through the local cellular base-station during the time that handoff is taking place. This approach can eliminate VHO link loss. It is shown that the act of WLAN-to-cellular handoff can result in a severe bandwidth deficit problem on the WLAN. A novel bandwidth reservation and securing mechanism is proposed which overcomes this problem and performs significantly better than schemes based on modified versions of the static guard channel scheme used in cellular networks. The work is characterized by simulation and analytic models which investigate the key performance aspects of this type of system. / Thesis / Doctor of Philosophy (PhD)

Fifth Generation (5G) introduces technologies that expedite the adoption of mobile networks, such as densely connected devices, ultra-fast data rate, low latency and more. With those visions in 5G and 6G in the next step, the need for a higher transmission rate and lower latency is more demanding, possibly breaking Moore’s law. With Artificial Intelligence (AI) techniques becoming mature in the past decade, optimizing resource allocation in the network has become a highly demanding problem for Mobile Network Operators (MNOs) to provide better Quality of Service (QoS) with less cost. This thesis proposes a Reinforcement Learning (RL) solution on bandwidth allocation for network slicing integration in disaggregated Open Radio Access Network (O-RAN) architecture. O-RAN redefines traditional Radio Access Network (RAN) elements into smaller components with detailed functional specifications. The concept of open modularization leads to greater potential for managing resources of different network slices. In 5G mobile networks, there are three major types of network slices, Enhanced Mobile Broadband (eMBB), Ultra-Reliable Low Latency Communications (URLLC), and Massive Machine Type Communications (mMTC). Each network slice has different features in the 5G network; therefore, the resources can be relocated depending on different needs. The virtualization of O-RAN divides the RAN into smaller function groups. This helps the network slices to divide the shared resources further down. Compared to traditional sequential signal processing, allocating dedicated resources for each network slice can improve the performance individually. In addition, shared resources can be customized statically based on the feature requirement of each slice. To further enhance the bandwidth utilization on the disaggregated O-RAN, a RL algorithm is proposed in this thesis on midhaul bandwidth allocation shared between Centralized Unit (CU) and Distributed Unit (DU). A Python-based simulator has been implemented considering several types of mobile User Equipment (UE)s for this thesis. The simulator is later integrated with the proposed Q-learning model. The RL model finds the optimization on bandwidth allocation in midhaul between Edge Open Cloud (O-Cloud)s (DUs) and Regional O-Cloud (CU). The results show up to 50% improvement in the throughput of the targeted slice, fairness to other slices, and overall bandwidth utilization on the O-Clouds. In addition, the UE QoS has a significant improvement in terms of transmission time.

In this thesis we investigate the convergence rate of gamma kernel estimators in recursive density estimation. Unlike the traditional symmetric and fixed function, the gamma kernel is a kernel function with bounded support and varying shapes. Gamma kernels have been used to address the boundary bias problem which occurs when a symmetric kernel is used to estimate a density which has support on [0, ?). The recursive density estimation is useful when an 'additional data' (on-line) comes from the population density which we want to estimate. We utilize the ideas and results from the adaptive kernel estimation to show that the L_2 convergence rate of the recursive kernel density estimators which use gamma kernels is n^(-4/5).

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