Low-Complexity Joint Channel Estimation and List Decoding of Short Codes

A pilot-assisted transmission (PAT) scheme is proposed for short blocklengths, where the pilots are used only to derive an initial channel estimate for the list construction step. The final decision of the message is obtained by applying a non-coherent decoding metric to the codewords composing the list. This allows one to use very few pilots, thus reducing the channel estimation overhead. The method is applied to an ordered statistics decoder for communication over a Rayleigh block-fading channel. Gains of up to $1.2$ dB as compared to traditional PAT schemes are demonstrated for short codes with QPSK signaling. The approach can be generalized to other list decoders, e.g., to list decoding of polar codes.Comment: Accepted at the 12th International ITG Conference on Systems, Communications and Coding (SCC 2019), Rostock, German

Successive Cancellation Decoding of Single Parity-Check Product Codes

We introduce successive cancellation (SC) decoding of product codes (PCs) with single parity-check (SPC) component codes. Recursive formulas are derived, which resemble the SC decoding algorithm of polar codes. We analyze the error probability of SPC-PCs over the binary erasure channel under SC decoding. A bridge with the analysis of PCs introduced by Elias in 1954 is also established. Furthermore, bounds on the block error probability under SC decoding are provided, and compared to the bounds under the original decoding algorithm proposed by Elias. It is shown that SC decoding of SPC-PCs achieves a lower block error probability than Elias' decoding

Successive Cancellation Ordered Search Decoding of Modified GN\boldsymbol{G}_N-Coset Codes

A tree search algorithm called successive cancellation ordered search (SCOS) is proposed for $\boldsymbol{G}_N$-coset codes that implements maximum-likelihood (ML) decoding with an adaptive complexity for transmission over binary-input AWGN channels. Unlike bit-flip decoders, no outer code is needed to terminate decoding; therefore, SCOS also applies to $\boldsymbol{G}_N$-coset codes modified with dynamic frozen bits. The average complexity is close to that of successive cancellation (SC) decoding at practical frame error rates (FERs) for codes with wide ranges of rate and lengths up to $512$ bits, which perform within $0.25$ dB or less from the random coding union bound and outperform Reed--Muller codes under ML decoding by up to $0.5$ dB. Simulations illustrate simultaneous gains for SCOS over SC-Fano, SC stack (SCS) and SC list (SCL) decoding in FER and the average complexity at various SNR regimes. SCOS is further extended by forcing it to look for candidates satisfying a threshold on the likelihood, thereby outperforming basic SCOS under complexity constraints. The modified SCOS enables strong error-detection capability without the need for an outer code. In particular, the $(128, 64)$ PAC code under modified SCOS provides gains in overall and undetected FER compared to CRC-aided polar codes under SCL/dynamic SC flip decoding at high SNR.Comment: 14 pages, 9 figures, 3 tables. Submitted to IEEE journal. The revised version of the first submission. Major changes: 1) No dedicated section for numerical results. Instead, simulations are provided right after the relevant section. 2) More simulation results are added to compare all the state of art polar decoders in terms of the number of arithmetic operations. arXiv admin note: text overlap with arXiv:2105.0404

Short Packets over Block-Memoryless Fading Channels: Pilot-Assisted or Noncoherent Transmission?

We present nonasymptotic upper and lower bounds on the maximum coding rate achievable when transmitting short packets over a Rician memoryless block-fading channel for a given requirement on the packet error probability. We focus on the practically relevant scenario in which there is no \emph{a priori} channel state information available at the transmitter and at the receiver. An upper bound built upon the min-max converse is compared to two lower bounds: the first one relies on a noncoherent transmission strategy in which the fading channel is not estimated explicitly at the receiver; the second one employs pilot-assisted transmission (PAT) followed by maximum-likelihood channel estimation and scaled mismatched nearest-neighbor decoding at the receiver. Our bounds are tight enough to unveil the optimum number of diversity branches that a packet should span so that the energy per bit required to achieve a target packet error probability is minimized, for a given constraint on the code rate and the packet size. Furthermore, the bounds reveal that noncoherent transmission is more energy efficient than PAT, even when the number of pilot symbols and their power is optimized. For example, for the case when a coded packet of $168$ symbols is transmitted using a channel code of rate $0.48$ bits/channel use, over a block-fading channel with block size equal to $8$ symbols, PAT requires an additional $1.2$ dB of energy per information bit to achieve a packet error probability of $10^{-3}$ compared to a suitably designed noncoherent transmission scheme. Finally, we devise a PAT scheme based on punctured tail-biting quasi-cyclic codes and ordered statistics decoding, whose performance are close ($1$ dB gap at $10^{-3}$ packet error probability) to the ones predicted by our PAT lower bound. This shows that the PAT lower bound provides useful guidelines on the design of actual PAT schemes.Comment: 30 pages, 5 figures, journa

Successive Cancellation Inactivation Decoding for Modified Reed-Muller and eBCH Codes

A successive cancellation (SC) decoder with inactivations is proposed as an efficient implementation of SC list (SCL) decoding over the binary erasure channel. The proposed decoder assigns a dummy variable to an information bit whenever it is erased during SC decoding and continues with decoding. Inactivated bits are resolved using information gathered from decoding frozen bits. This decoder leverages the structure of the Hadamard matrix, but can be applied to any linear code by representing it as a polar code with dynamic frozen bits. SCL decoders are partially characterized using density evolution to compute the average number of inactivations required to achieve the maximum a-posteriori decoding performance. The proposed measure quantifies the performance vs. complexity trade-off and provides new insight into dynamics of the number of paths in SCL decoding. The technique is applied to analyze Reed-Muller (RM) codes with dynamic frozen bits. It is shown that these modified RM codes perform close to extended BCH codes.Comment: Accepted at the 2020 ISI

Design analysis and development of a high temperature actuator for gas turbine blade tip clearance control

During a typical startup cycle industrial gas turbine blades experience rapid radial thermal expansion while bulky shroud structure with larger thermal inertia requires much longer period to reach its operating temperature. Turbine designers have to leave a safe radial distance in order to prevent contact of blades to the surrounding annular casing. However, when thermal steady state in the turbine stage is achieved, shroud and casing grow and excessive amount of blade-shroud clearance remains. Engine efficiency is very sensitive to blade-shroud clearance. Just one millimeter of radial blade tip gap in fist stage turbine section of a 150 MW class engine leads to 4% efficiency drop due to blade tip leakage. To achieve better efficiency or higher power, turbine blade tip clearance has to be controlled. Attempts to address blade tip clearance problem were not applicable as designs were bulky and complex which required excessive modification on the turbine hardware and design. The goal of this study is to design, analyze and develop a low-cost and compact actuator system which is capable of controlling the tip clearance up to 0.25mm at elevated temperatures. Actuator will be positioned between inner and outer shrouds of the casing to force the inner shroud radially away from the blades during transients, and allow it to come back towards the blades when casing reaches operating temperature to decrease the tip leakage during steady state. Different actuator designs have been studied and finite element analysis solutions have been obtained for deflection and stress. Low cycle fatigue life of the actuator has been estimated via Coffin-Manson criterion. An experimental setup has been designed and fabricated to validate the simulation results. Furthermore, since actuator will be subjected to wear at elevated temperatures due to mechanical loading and vibrations in the gas turbine, friction and wear behavior of candidate actuator materials has to be investigated. High temperature scuffing combined with rapid oxidation can lead to failures and dramatic reductions service life. Therefore, another experimental setup has been developed to conduct friction and wear tests of the candidate actuator materials, i.e. Nickel and Cobalt based superalloys Haynes 25, 188 and 214. The tests have been conducted at 20, 200,400 and 540 °C. Overall, the results indicated that the compact actuator can achieve 0.25 mm tip clearance reduction leading to 1% efficiency increase for 880 startup cycles

Ebû Naîm Ahmed el-Hâdimî’in Risâle fî efʿâli’l-ʿibâd Adlı Risâlesinin İnceleme, Tahkik ve Tercümesi

Çalışmamız, Ebû Naîm Ahmed el-Hâdimî’nin (ö. 1160/1744) Risâle fî efʿali’l-ʿibâd adlı risâlesi üzerinden müellifin insan fiilleri hakkındaki yaklaşımları konumlandırmaya ilişkin ortaya koyduğu tespitleri inceleyecektir. Ayrıca risâlenin meseleye katkı sağlayan özgün yönlerine de işaret edilecektir. Bunların yanı sıra tahkik ve tercümesi de yapılmak suretiyle risâlenin literatüre kazandırılması hedeflenmektedir. İnsan fiilleri ve irâde-i cüzʾiyye hakkında İslam tarihi boyunca birçok yaklaşım neşet etmiştir. Buna paralel olarak bu yaklaşımların birbirinden ayrışma ve ortak noktalarını tespit etmeye ve bunları konumlandırmaya çalışan bir yazım literatürü de gelişmiştir. Çalışmamıza konu olan muhtasar nitelikteki bu risâle ise bu literatürün bir hasılası olarak görülebilir. Müellifin Celâluddin Devvânî (ö. 908/1502), Seyyid Şerif Cürcânî (ö. 816/1413) ve Sadrüşşerîʿa es-Sânî’yi (ö. 747/1346) fiiller konusunda yaygın Mâtürîdî ve Eşʿarî gelenekten farklı şekilde konumlandırması risâlenin dikkat çeken yönlerinden birisidir

Faktör V leiden mutasyonu olan mitral valv replasmanlı hastada erken dönemde mitral stuck kapak gelişimi

Nefes darlığı sebebi ile kardiyoloji polikliniğine başvuran 52 yaşındaki kadın hastanın hikâyesinde 3 ay önce mitral darlık sebebi ile MVR mitral valv replasmanı operasyonu geçirdiği ve Faktör V Leiden homozigot taşıyıcısı olduğu öğrenildi. Antikogulan tedavi rejimi varfarin şeklinde seçilmiş olan hastaya yapılan kardiyolojik muayene ve TTE transtorasik ekokardiyografi sonucunda mitral pozisyondaki protez kapak üzerinde gradiyent artışı, kapak hareketlerinde disfonksiyon ve pulmoner hipertansiyon saptandı. Sinef- loroskopi ile mitral pozisyondaki protez kapak liflet hareketlerinin son derece kısıtlandığı gözlenen hastaya erken dönemde gelişen stuck hareketsiz mitral kapak nedeniyle acil re-do MVR planlandı. Operasyonda trombotik pannusun kapağın her iki lifletine doğru genişlediği ciddi hareket kısıtlılığı yaptığı görülerek çıkartıldı. Yerine 27 mm St.Jude mekanik biliflet kapak replasmanı yapıldı. Hasta medikal tedavisi ve varfarin terapötik dozu düzenlenerek postoperatif 10. günde taburcu edildi. Olgumuzdaki gibi tromboza eğilimin bilindiği genetik yapıdaki hastalarda protez kapak replasmanı sonrasında etkin antikoagulan tedavi kontrollerinin de sık ve düzenli yapılması gerektiğini düşünmekteyi