Browsing by Author "Dizdar, Onur"
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Item Open Access High throughput decoding methods and architectures for polar codes with high energy-efficiency and low latency(Bilkent University, 2017-11) Dizdar, OnurPolar coding is a low-complexity channel coding method that can provably achieve Shannon’s channel capacity for any binary-input discrete memoryless channels (B-DMC). Apart from the theoretical interest in the subject, polar codes have attracted attention for their potential applications. We propose high throughput and energy-efficient decoders for polar codes using combinational logic targeting, but not limited to, next generation communication services such as optical communications, Massive Machine-Type Communications (mMTC) and Terahertz communications. First, we propose a fully combinational logic architecture for Successive-Cancellation (SC) decoding, which is the basic decoding method for polar codes. The advantages of this architecture are high throughput, high energy-efficiency and flexibility. The proposed combinational SC decoder operates at very low clock frequencies compared to synchronous (sequential logic) decoders, but takes advantage of the high degree of parallelism inherent in such architectures to provide a higher throughput and higher energy-efficiency compared to synchronous implementations. We provide ASIC and FPGA implementation results to present the characteristics of the proposed architecture and show that the decoder achieves approximately 2.5 Gb/s throughput with a power consumption of 190 mW with 90 nm 1.3 V technology and block length of 1024. We also provide analytical estimates for complexity and combinational delay of such decoders. We explain the use of pipelining with combinational decoders and introduce pipelined combinational SC decoders. At longer block lengths, we propose a hybrid-logic SC decoder that combines the advantageous aspects of the combinational and synchronous decoders. In order to improve the throughput further, we use weighted majority-logic decoding for polar codes. Unlike SC decoding, majority-logic decoding fails to achieve channel capacity, but offers better throughput due its parallelizable schedule. We give a novel recursive description for weighted majority-logic decoding for bit-reversed polar codes and use the proposed definition for implementations without determining the check-sums individually as done in conventional majoritylogic decoding. We demonstrate by analytical estimates that the complexity and latency of the proposed architecture are O(Nlog2 3) and O(log2 2 N), respectively. Then, we validate the calculated estimates by a fully combinational logic implementation on ASIC. For a block length of 256, the implemented decoders achieve 17 Gb/s throughput with 90 nm 1.3 V technology. In order to compensate the error performance penalty of the majority-logic decoding, we propose novel hybrid decoders that combine SC and weighted majority-logic decoding algorithms. We demonstrate that very high latency gains can be obtained by such decoders with small error performance degradation with respect to SC decoding.Item Open Access Ida M Tarbell : the historian(Bilkent University, 2010) Dizdar, OnurThis thesis focuses on Ida M. Tarbell, one of the most influential literary figures of the late 19th and early 20th century in the United States. She has been recognized as the pioneer of investigative journalism and generally referred to as a muckraker. This study, however, will argue that she was primarily a historian. By putting her two significant historical works, Life of Lincoln and The History of the Standard Oil Company, into the center of analysis and by exploring her career in general, it will try to demonstrate Tarbell’s qualities as a historian and her contribution to the history discipline. In general terms, it aspires to explore Tarbell’s position in American literary, social and economic history.Item Open Access Performance of edge windowing for OFDM under non-linear power amplifier effects(IEEE, 2017) Göken, Çağrı; Dizdar, OnurEdge windowing is a windowing technique for Orthogonal Frequency Division Multiplexing (OFDM) signals based on the idea of using shorter cyclic prefix (CP) and longer window lengths at the edge subcarriers while keeping the symbol length fixed. In this study, we investigate the performance of OFDM signals with edge windowing under non-linear power amplifier (PA) effects by observing out-of-band (OOB) emission characteristics, average error vector magnitude (EVM) and coded block error rate (BLER) performance. We explore whether the possible gains over conventional windowing in the presence of PA is possible. We show that the edge windowing can still provide improvements over conventional windowing in terms of OOB emission suppression under various PA models at the expense of increased average EVM, whereas the channel coding substantially mitigates the performance loss due to inter-symbol and inter-carrier interference (ISI-ICI) effects arising as a result of shorter CP length at the edge subcarriers.