Frequency-Domain Hammerstein Self-Interference Canceller for In-Band Full-Duplex OFDM Systems

In-band full-duplex communications have been spotlighted because they can double the spectral efficiency of the current wireless communication systems. However, it is necessary to mitigate the self-interference (SI). Currently, several time-domain and frequency-domain SI cancellers have been proposed. Timedomain SI cancellers are based on the parallel Hammerstein (PH) model, and they have good flexibility with high computational cost. In contrast, frequency-domain SI cancellers can achieve high cancellation performance with low computational cost but they have less flexibility than time-domain PH based SI cancellers. In this paper, we propose a frequency-domain SI canceller based on the PH model. The proposed scheme estimates the frequency response of the SI channel and regenerates SI signals by the overlap-save method. Therefore, the computational complexity of the proposed scheme is less than time-domain PH based SI canceller. The performance of the proposed scheme is assessed by equivalent baseband signal simulations of a fullduplex transceiver. As a result, the proposed scheme achieves high SI cancellation as the time-domain PH based SI canceller with low computational cost. In addition, the convergence performance of the proposed scheme is faster than the time-domain scheme

Basis Function Selection of Frequency-Domain Hammerstein Self-Interference Canceller for In-Band Full-Duplex Wireless Communications

This paper presents a basis function selection technique of a frequency-domain Hammerstein digital selfinterference canceller for in-band full-duplex communications. The power spectral density (PSD) of the nonlinear selfinterference signal is theoretically analyzed in detail, and a nonlinear self-interference PSD estimation method is developed. The proposed selection technique decides on the basis functions necessary for cancellation and relaxes the computational cost of the frequency-domain Hammerstein canceller based on the estimated PSD of the self-interference of each basis function. Furthermore, the convergence performance of the canceller is improved by the proposed selection technique. Simulation results are then presented, showing that the proposed technique can achieve similar cancellation performance compared with the original frequency-domain Hammerstein canceller and a time-domain nonlinear canceller. Additionally, it is shown that the proposed technique improves the computational cost and the convergence performance of the original frequency-domain Hammerstein canceller

第2学年「組織学総論」・「基礎神経科学」の教育効果の検討 ─中間試験導入と事前・事後学習課題の提示─

獨協医科大学医学部では平成27年度より，発展的に自己学習習慣を身につけさせるため，講義時間・カリキュラムの変更を行っている.この効果を検討するため，変更前の2 年間 （平成25 年度および平成26 年度） と変更後の2年間 （平成27年度および平成28年度） の「組織学総論」および「基礎神経科学」の試験結果を比較し解析した．対象は，平成25年度138 名，平成26年度129 名，平成27年度133 名，平成28年度121 名の2年生である．事後学習課題の提出・評価，中間試験成績，学期末試験成績の結果とそれぞれの関連を解析した．特に中間試験を形成的評価と位置づけ，総合的評価としての学期末試験に及ぼす影響について検討した．形成的評価として中間試験を取り入れることにより，学生の学習方法の改善と学習意欲を促し学期末試験結果が向上した．事前・事後学習課題の提示は，知識の定着に有効であった．また，課題の評価と成績は関連しなかったが，未提出や期限切れ提出を繰り返す学生が成績不良となることが多く，事前・事後学習課題の提示は，早期指導介入のスクリーニングとして有効であると考えられた．Dokkyo Medical University made lecture time and curriculum changes, in effect since the 2015-16 school year, to help students learn self-study habits for their development. To examine the effectiveness of these changes, test results of “Introduction to Histology” and “Basic　Neuroscience” for the two years after the changes （i.e., the 2015-16 and 2016-17 school years）were compared to those of the two years before the changes （2013-14 and 2014-15） and analysis was performed. The comparison focused on second-year students, including 138 in 2013-14, 129 in 2014-15, 133 in 2015-16, and 121 in 2016-17. The correlations among post-class homework submission and scores, midterm test grades, and end-of-term test grades were analyzed. In particular, midterm tests （objective tests）were treated as formative scores and their effect on end-of-term tests（general scores）was examined. By introducing midterm tests（objective tests）as formative scores, the courses helped students/learners to improve their study methods, motivated them to study, and resulted in higher grades during end-of-term tests. Assigning preclass and post-class homework was an effective way to firmly establish knowledge. Additionally, though there was no correlation between homework scores and grades, students who repeatedly failed to submit homework or submitted it late often got poor grades, meaning that homework evaluation seems to be effective screening for earlyguidance and intervention

Weighted Least Squares with Orthonormal Polynomials and Numerical Integration for Estimation of Memoryless Nonlinearity

The nonlinearity of amplifiers is one of the major impairments in wireless communications. In this letter, we propose a novel estimation method for the memoryless nonlinearity of amplifiers using weighted least squares and provide its theoretical error analysis on complex Gaussian signals. In the proposed method, the input signal and weight value are obtained via numerical integration formulas. Simulation results show that the proposed method can achieve a sufficiently low reconstruction error with 10 measurement samples on the estimation of the 13th-order nonlinearity. In addition, the simulation and theoretical results are consistent with each other

Iterative Nonlinear Self-Interference Cancellation for In-Band Full-Duplex Wireless Communications Under Mixer Imbalance and Amplifier Nonlinearity

This paper presents an iterative estimation and cancellation technique for nonlinear in-band full-duplex transceivers with IQ imbalances and amplifier nonlinearities. The estimation process of the proposed scheme consists of three stages, namely, the channel response estimation, IQ imbalance estimation, and power amplifier and low-noise amplifier (LNA) nonlinearities estimation. For the estimation of the parameters and improvement of the accuracy, distortions are compensated by cancellation or inversion with the latest estimated parameters. On the one hand, the channel response is estimated on the time domain; on the other hand, the IQ imbalance and nonlinearities are estimated on the frequency domain for a more straightforward estimation and superior accuracy. In the cancellation process of the proposed scheme, the received signal is compensated with the estimated parameters of the LNA and receiver IQ imbalance before cancellation because the desired signal is received with a high-power self-interference and is distorted by the radiofrequency receiver impairments. Simulation results show that the proposed technique can achieve higher cancellation performance compared with the Hammerstein canceller when the LNA is saturated by the self-interference. Additionally, the performance of the proposed canceller converges much faster than that of the Hammerstein canceller

ものつくり大学同窓会 平成24年度 地域貢献活動報告

2012 年度にものつくり大学同窓会が実施した「ボランティア活動」ならびに「ものつくり体験教室」について報告する