Recently Added Theses
View AllFPGA'lerin hızlı, güvenli ve uzaktan çoklu yüklenmesi
The purpose of this thesis is to develop an efficient framework to implement secure FPGA-based (Field Programmable Gate Array) systems. An FPGA is a reconfigurable device that has the ability to adapt the hardware during runtime by loading a new circuit on the reconfigurable fabric. However, a circuit design formed as configuration data (bitstream) can be easily counterfeited and needs to be protected against the risks of cloning, overbuilding, and reverse-engineering. Although many applications could be implemented on low-cost FPGAs, protection schemes and dedicated hardware are mostly available on high-end FPGAs. In addition to this, only high-end FPGAs support dynamic partial self reconfiguration (DPSR), which is the ability tochange a part of a design at runtime. This thesis focuses on developing a security scheme leveraging hardware intrinsic features on low-cost FPGAs by using physical unclonable functions (PUFs). A PUF provides a way to extract security keys which are unique to each device. This thesis combines PUFs with another security scheme called obfuscation. Obfuscation is the act of intentionally modifying the description or structure of a circuit in order to conceal its functionality. Obfuscation is implemented in this thesis at RTL-level and is used to authenticate and control the device by using the keys by exploiting the PUF technique within a finite state machine (FSM). These methods are further used to implement ?secure MultiBoot?. The MultiBoot feature allows to reconfigure the FPGA fully at runtime as opposed to DPSR for devices which do not support partial reconfiguration. This thesis also establishes a framework that enables secure remote MultiBoot. A bitstream compression technique is applied to reduce the transmission time over the network. A proof-of-concept example is implemented using the proposed framework.
Yarı rezonans yapı ve yayılmış tayf metodu ile indüksiyon ocak tasarımı ve deneysel sonuçları
This thesis presents an induction cooker design and its detailed experimental results. The design is based on Quasi Resonant Topology and is unique in terms of the particular Jitter Method it employs to drive the semiconductor switches (IGBTs).Most induction cookers are based on Half Bridge Topology. Although Quasi Resonant Topology offers a more cost effective implementation, it introduces more EMI problems. However, we solve these problems with our Jitter Method. Although there are other works in the literature that solve the EMI issues by some sort of jitter methods (i.e., spread spectrum methods), these methods do not address the high voltage stress created across the IGBTs. However, the Jitter Method proposed in this thesis also reduces collector-emitter voltage stress besides improving EMI. Note that jitter methods also prevent mechanical vibration (i.e., resonance), which cause audible noise.Another thing that makes this thesis unique in the literature is the rich set of experimental results it contains ? based on an experimental prototype we built with a power rating of 2300W. While the existing literature mostly contains theoretical treatment, we have produced detailed experimental results for Quasi Resonant Topology and show that the current harmonics (drawn from the utility) stay within the published standards (TS EN 61000-3-2). We also include experimental results for Delivered Power Detection, Pan Detection, and Protection Circuits.
Çoklu-seçim dönmeli iş düzenleyici
In this thesis, we propose two multi(m)-pick Round Robin Arbiter (RRA) architectures. An m-pick RRA selects the m topmost requests out of n inputs with priority order indicated by an internally kept pointer (with an update policy that ensures fairness among requestors). The architectures that we propose are m-pick Thermo Coded-Parallel Prefix Arbiter (TC-PPA) and Three-Dimensional Programmable m-Selector RRA (3DPmS-RRA). Prior to this thesis, these two architectures existed in the literature as 2-pick and 1-pick arbiters, respectively. Our main contribution to the literature is the generalization of these architectures to m-pick. A logic building block that we call ?Saturated Adder? plays a key role in this generalization, which makes the 1-pick and 2-pick architectures simply special cases. We developed six differentvariants of 3DPmS-RRA and eight different variants of m-pick TC-PPA. We wrote automated HDL code generators for all variants as well as Cascade Architecture, which is a straight-forward way of implementing a multi-pick RRA using 1-pickProgrammable Priority Encoders. Then, all multi-pick architectures were verified and synthesized. Our experimental results show that 3DPmS-RRA architecture is the best choice for all pick sizes (except 2-pick) when timing is the primary design criterion. However, when area is more critical, TC-PPA architecture performs better. It is worthwhile to note that in terms of timing 3DPmS-RRA is better than TC-PPA by a mere 8% at the most based on our synthesis results. However, when we consider area, TC-PPA has significant improvements over 3DPmS-RRA, up to 53%.
ALTO servisli eş görevli ağlarda gerçek zamanlı ölçeklenebilir video akıtımı
It has been measured that, as high as 80% of the average Internet traffic is now from peer-to-peer (P2P) applications, and upwards of 90% during peak hours. These results tell us that a significant portion of the traffic that ISPs route is P2P traffic. However, since the typical P2P application overlay network model is network-oblivious, due to its nature, it causes inefficient network utilization, and low qualityof experience, from the perspective of the network providers and the end users, respectively. This inefficient resource utilization increases inter-ISP traffic, and leads to serious disruptions on ISP economics as well as lower QoE by the users.A significant portion of the P2P traffic on the Internet is for video applications. Furthermore, real networks are heterogeneous in link rates. Thus a live video streamingservice should support streams with different qualities for users using different data rates. A possible solution to this problem is achieved by creating a different video file for each quality level. However, this solution is inefficient due to data duplication.To improve ISP economics, improve network efficiency and achieve acceptable QoE performance, we implement a P2P Live Scalable Video Streaming Mechanism and Application Layer Traffic Optimization (ALTO) Server, by using different peer ranking algorithms in this thesis. The main objective of this thesis, to show that the ALTO protocol reduces the inter-ISP traffic significantly while maintaining the application performance. Results reveal that, placing an ALTO Server decreases the inter-ISP traffic dramatically while maintaining a satisfactory QoE performance for the streaming video application.
Performance analysis and optimization of relay-assisted free space optical communication systems
Free-space optical (FSO) communication has received an increasing attention in recent years with their ability to achieve ultra-high data rates (at the order of multiple gigabits per second) over unlicensed optical spectrum. A major degrading factor, particularly in long links, is the atmospheric turbulence induced fading. Smartly exploiting the fact that fading variance is distance-dependent in FSO channel, relay assisted transmission takes advantage of the resulting shorter hops and yields significant performance improvements. In this thesis, we make several contributions to the performance analysis and design of relay-assisted FSO systems. In the first part, we investigate how to determine optimal relay locations in serial and parallel FSO relaying as to minimize the outage probability and quantify performance improvements obtained through optimal relay placement. In the second part, we investigate the combined use of serial and parallel relaying for FSO mesh networks. We derive the outage probability expressions of FSO mesh networks and demonstrate performance improvements with respect to both stand-alone serial and parallel relaying schemes. We also present a diversity gain analysis and quantify the achievable diversity orders in terms of the number of relays and turbulence channel parameters. Finally, we investigate the use of all-optical relaying removing the need for optical-electrical and electrical-optical conversions. Building on all-optical relay assumption, we investigate the outage performance of a dual-hop FSO link taking into account practical limitations such as amplifier noise and filtering effects.
Femto-hücre ağlarında en düşük inen bağlantı girişimi için ortak frekans tahsisi ve güç kontrolü
Due to the fact that the most of data services and more than half of calls are requested indoors, it has been dramatically important and even a must for cellular operators to provide more than adequate indoor coverage. Instead of expensive traditional approach which is to use outdoor macrocell base stations to provide good indoor coverage, indoor systems for the cases of small offices and homes are found more convenient and efficient.Femtocell is one of the developing technologies as a recent solution to aforementioned problems. They offer to improve the indoor coverage and reduce the cellular network load. However, in case of the most feasable solution, co-channel deployment of the femtocell network over the existing macrocell network, a closed access approach could result in serious co-channel interference problems.In this thesis, improvements to the performances of both femtocell and indoor macrocellular users in terms of average achieved data rates are considered. A joint spectrum and power control algorithm is proposed to mitigate the co-tier and cross-tier interferences. The algorithm aims to save the indoor macrocell subscribers from the violation of femtocells whilst providing throughput to femtocell subscribers as higher as possible. Simulations including physical layer and system level are conducted to determine the performance of the proposed method. Results reveal that an algorithm that combines the management of two important resources, spectrum and power, performs really well in two-tier networks, even better than the techniques managing only one resource, in terms of overall system performance.