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∏-COHERENT DIMENSIONS AND ∏-COHERENT RINGS

  • Mao, Lixin
    • Journal of the Korean Mathematical Society
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    • v.44 no.3
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    • pp.719-731
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    • 2007
  • R is called a right ${\Pi}-coherent$ ring in case every finitely generated torsion less right R-module is finitely presented. In this paper, we define a dimension for rings, called ${\Pi}-coherent$ dimension, which measures how far away a ring is from being ${\Pi}-coherent$. This dimension has nice properties when the ring in question is coherent. In addition, we study some properties of ${\Pi}-coherent$ rings in terms of preenvelopes and precovers.

A Comparison with SNR Performance of Coherent Integration and Non-coherent Integration to Estimate Target Detection Range in Radar System (레이더 시스템에서 목표물 탐지 거리 추정을 위한 코히런트 집적과 비 코히런트 집적의 SNR 성능 비교)

  • Ga, Gwan-U;Ham, Sung-Min;Lee, Kwan-Hyeong
    • The Journal of Korea Institute of Information, Electronics, and Communication Technology
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    • v.7 no.2
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    • pp.86-91
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    • 2014
  • This paper compare with SNR performance of coherent integration and non-coherent integration in radar system. This paper to prevent distortion of transmit signal and radar return in radar system is used to pulsed waveform. This paper to estimate target detection range and to compare with SNR performance used to coherent integration performed before the envelope detector and non-coherent integration processed after the envelope detector. Through simulation, SNR performance of coherent integration and non-coherent integration were comparatively analyzed. SNR performance of coherent integration is good proof higher than non-coherent integration.

Nil-COHERENT RINGS

  • Xiang, Yueming;Ouyang, Lunqun
    • Bulletin of the Korean Mathematical Society
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    • v.51 no.2
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    • pp.579-594
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    • 2014
  • Let R be a ring and $Nil_*$(R) be the prime radical of R. In this paper, we say that a ring R is left $Nil_*$-coherent if $Nil_*$(R) is coherent as a left R-module. The concept is introduced as the generalization of left J-coherent rings and semiprime rings. Some properties of $Nil_*$-coherent rings are also studied in terms of N-injective modules and N-flat modules.

Performance Comparison of Coherent and Non-Coherent Detection Schemes in LR-UWB System

  • Kwon, Soonkoo;Ji, Sinae;Kim, Jaeseok
    • Journal of Communications and Networks
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    • v.14 no.5
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    • pp.518-523
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    • 2012
  • This paper presents new coherent and non-coherent detection methods for the IEEE 802.15.4a low-rate ultra-wideband physical layer with forward error correction (FEC) coding techniques. The coherent detection method involving channel estimation is based on the correlation characteristics of the preamble signal. A coherent receiver uses novel iterated selective-rake (IT-SRAKE) to detect 2-bit data in a non-line-of-sight channel. The non-coherent detection method that does not involve channel estimation employs a 2-bit data detection scheme using modified transmitted reference pulse cluster (M-TRPC) methods. To compare the two schemes, we have designed an IT-SRAKE receiver and a MTRPC receiver using an IEEE 802.15.4a physical layer. Simulation results show the performance of IT-SRAKE is better than that of the M-TRPC by 3-9 dB.

A Study on Target Direction and Rage Estimation using Radar Single Pulse (레이더 단일 펄스를 이용한 목표물 방향과 거리 추정에 대한 연구)

  • Lee, Kwan-Hyeong
    • The Journal of the Institute of Internet, Broadcasting and Communication
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    • v.14 no.6
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    • pp.107-112
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    • 2014
  • In this paper, we analysed a performance signal to noise ratio about pulse, integration coherent, and integration non coherent system in radar system. It compared existing with proposal method in order to estimation two target direction of arrival. Generally, radar system radiate pulse wave in order to decreasing distortion of return wave and transmission wave. We analysed the performance integration coherent and integration non coherent. Integration coherent is processing system before doing envelop detection, and integration non coherent is processing system after doing envelop detection. Through simulation, we analysed a performance signal to noise ratio to estimation two target range detection and estimated target direction of arrival. We showed that integration coherent system is the most good performance.

Evolution Properties of a Partially Coherent Flat-topped Vortex Hollow Beam Propagating in Uniaxial Crystals Orthogonal to the Optical Axis

  • Liu, Dajun;Wang, Guiqiu;Luo, Xixian;Yin, Hongming;Wang, Yaochuan
    • Journal of the Optical Society of Korea
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    • v.20 no.6
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    • pp.686-693
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    • 2016
  • The analytical expressions for a partially coherent flat-topped vortex hollow beam propagating in uniaxial crystals orthogonal to the optical axis are derived, and the intensity and coherent vortex properties of partially coherent flat-topped vortex hollow beam propagation in uniaxial crystals orthogonal to the optical axis are analyzed by numerical examples. The influence of beam order parameter N, topological charge M, the coherence length and the ratio of refractive indices $n_e/n_o$ of uniaxial crystals on the normalized intensity distribution and coherent vortex of a partially coherent flat-topped vortex hollow beam propagating in uniaxial crystals are discussed in detail.

σ-COHERENT FRAMES

  • Lee, Seung On
    • Journal of the Chungcheong Mathematical Society
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    • v.14 no.1
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    • pp.61-71
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    • 2001
  • We introduce a new class of ${\sigma}$-coherent frames and show that HA is a ${\sigma}$-coherent frame if A is a ${\sigma}$-frame. Based on this, it is shown that a frame is ${\sigma}$-coherent iff it is isomorphic to the frame of ${\sigma}$-ideals of a ${\sigma}$-frame. Finally we show that ${\sigma}$-COhFrm and ${\sigma}$Frm are equivalent.

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COUNTABLY APPROXIMATING FRAMES

  • Lee, Seung-On
    • Communications of the Korean Mathematical Society
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    • v.17 no.2
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    • pp.295-308
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    • 2002
  • Using the Countably way below relation, we show that the category $\sigma$-CFrm of $\sigma$-coherent frames and $\sigma$-coherent homomorphisms is coreflective n the category Frm of frames and frame homomorphisms. Introducting the concept of stably countably approximating frames which are exactly retracts of $\sigma$-coherent frames, it is shown that the category SCAFrm of stably countably approximating frames and $\sigma$-proper frame homomorphisms is coreflective in Frm. Finally we introduce strongly Lindelof frames and show that they are precisely lax retracts of $\sigma$-coherent frames.

Cell ID Detection Schemes Using PSS/SSS for 5G NR System (5G NR 시스템에서 PSS/SSS를 이용한 Cell ID 검출 방법)

  • Ahn, Haesung;Kim, Hyeongseok;Cha, Eunyoung;Kim, Jeongchang
    • Journal of Broadcast Engineering
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    • v.25 no.6
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    • pp.870-881
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    • 2020
  • This paper presents cell ID (cell identity) detection schemes using PSS/SSS (primary synchronization signal/secondary synchronization signal) for 5G NR (new radio) system and evaluates the detection performance. In this paper, we consider two cell ID detection schemes, i.e. two-stage detection and joint detection schemes. The two-stage detection scheme consists of two stages which estimate a channel gain between a transmitter and receiver and detect the PSS and SSS sequences. The joint detection scheme jointly detects the PSS and SSS sequences. In addition, this paper presents coherent and non-coherent combining schemes. The coherent scheme calculates the correlation value for the total length of the given PSS and SSS sequences, and the non-coherent combining scheme calculates the correlation within each group by dividing the total length of the sequence into several groups and then combines them non-coherently. For the detection schemes considered in this paper, the detection error rates of PSS, SSS and overall cell ID are evaluated and compared through computer simulations. The simulation results show that the joint detection scheme outperforms the two-stage detection scheme for both coherent and non-coherent combining schemes, but the two-stage detection scheme can greatly reduce the computational complexity compared to the joint detection scheme. In addition, the non-coherent combining detection scheme shows better performance under the additive white Gaussian noise (AWGN), fixed, and mobile environments.