Elektrik- Elektronik Mühendisliği
Permanent URI for this community
Browse
Browsing Elektrik- Elektronik Mühendisliği by Author "Afşer, Hüseyin."
Now showing 1 - 2 of 2
Results Per Page
Sort Options
Item Channel polarization with higher - order memory(Thesis (Ph.D.) - Bogazici University. Institute for Graduate Studies in Science and Engineering, 2016., 2016.) Afşer, Hüseyin.; Deliç, Hakan.Channel coding is one of the most fundamental problems regarding the nature of communication. Polar codes, developed by Ar kan, were the rst demonstration of practical channel codes that provably achieve theoretical limits in a wide range of communication scenarios. Based on simple channel transformations which are called channel combining and splitting, Ar kan developed the idea of channel polarization which resulted in polar codes. In this dissertation we focus on the unique properties of polar codes and channel polarization. First, we investigate the channel-speci c construction of polar codes, a point which discriminates polar codes from Reed-Muller (RM) codes. We obtain results showing the inherent e ect of the underlying channel on the construction of polar codes and provide a bridge between polar and RM codes. Our results easily extend to obtaining a characterization for the rate of polarization as well. Next, we consider practical uses of polar codes for fading channels. We design a bit-interleaved polar-coded modulation scheme (BIPCM) by deriving a low complexity code-construction method and designing a lower complexity successive cancellation list decoder (SCLD). We compare the resultant BIPCM system with the existing solutions and show that it provides signi cant performance advantages. Finally, we generalize the channel polarization idea by changing channel combining and splitting operations. By introducing a memory order in the channel combining process we obtain a class of codes, including the original ones, that are parametrized by the memory order. We show that the new family of polar codes achieve the theoretical limits as well and they can also be used with lower complexity by increasing the memory order. We thereby complement Ar kan's conjecture that channel polarization is in fact a general phenomenon.Item Finite difference beam propagation method for analyzing bend enhanced optical touch sensor(Thesis (M.S.)-Bogazici University. Institute for Graduate Studies in Science and Engineering, 2008., 2008.) Afşer, Hüseyin.; Yüksel, Heba.Analysis of waveguides by computational methods is very important and widely used in optical fiber communications since the power loss due to bending of the optical fibers decreases the channel capacity of the optical fiber links. These systems require proper analysis tools to understand the effects of corruption and degradation of the channel capacity resulting from external disturbances. Although telecommunication systems tries to analyze the corruption in the opti- cal waveguides such as power attenuation and channel degregation, optical waveguide based sensor applications trie to seek ways of using these changes or corruptions for sensing different properties of the environment. Since optical sensors carry some ad- vantages as being insensitive to electromagnetic interferance , having long durability and high precision; they deserve certain attention. The aim of this thesis is to provide an analysis method for electrical field and power propagation in waveguides undergoing severe bending by using finite difference beam propagation methods in three dimensions, where the waveguides are bent severely so that the considerable amount of power radiation occurs to the outside of the waveguide with the intention of sensing. As an application in this thesis we propose and analyze a bend enhanced optical touch sensor with the developed three dimensional finite difference beam propagation methods and validate our analysis and reason on the operability of this sensor.