• ETRI Journal
• /
• 제28권5호
• /
• pp.684-687
• /
• 2006

In this letter, we evaluate the system performance of a space-time block coded (STBC) multicarrier (MC) DS-CDMA system over a time selective fading channel, with imperfect channel knowledge. The average bit error rate impairment due to imperfect channel information is investigated by taking into account the effect of the STBC position. We consider two schemes: STBC after spreading and STBC before spreading in the MC DS-CDMA system. In the scheme with STBC after spreading, STBC is performed at the chip level; in the scheme with STBC before spreading, STBC is performed at the symbol level. We found that these two schemes have various channel estimation errors, and that the system with STBC before spreading is more sensitive to channel estimation than the system with STBC after spreading. Furthermore, derived results prove that a high spreading factor (SF) in the MC DS-CDMA system with STBC before spreading leads to high channel estimation error, whereas for a system with STBC after spreading this statement is not true.

• 한국전자파학회논문지
• /
• 제14권11호
• /
• pp.1134-1142
• /
• 2003

본 논문은 STS(Space Time Spreading) 다이버시티 기능을 지원하는 시스템을 FPGA(Field Programmable Gate Array)를 이용하여 구현하고, 이 시스템을 구성하고 있는 각 모듈의 기능과 실제 설계 방법을 소개한다. 본 논문에서 구현한 개루프 전송 다이버시티 시스템인 STS 시스템의 성능을 개선하기 위해서는 페이딩 환경에 따라 변화하는 통신채널의 정확한 검출이 필수적이다. 이를 위하여 파일럿 패널의 정확한 검출을 위한 최적의 망각인자(Forgetting factor)를 제안한다. 본 논문에서 구현한 STS 시스템과 컴퓨터 시뮬레이션을 통하여 CDMA2000 1x 신호환경에서 STS 시스템 적용시 도플러 주파수 80 Hz일 경우에 0.7의 값을 가지는 망각인자를 사용하여 각 구간의 페이딩을 검출함으로써 파일럿 신호의 전력이 충분하지 않을 경우에도 적분 구간을 많이 늘릴 필요 없이 파일럿 채널을 검출할 수 있음을 알 수 있었다.

• 한국산업정보학회논문지
• /
• 제11권4호
• /
• pp.112-120
• /
• 2006

다중 반송파 기술과 CDMA 기술이 결합된 MC-CDMA 시스템은 주파수 선택적 페이딩에 의한 신호감쇄를 완화시키면서 높은 전송률에 대한 요구를 만족시킬 수 있는 전송방식이다. 본 논문에서는 전송률이 서로 다른 다양한 서비스들을 지원하기 위한 새로운 비동기 MC-CDMA 시스템을 제안한다. 제안한 시스템에서는 W-CDMA 하향링크에 사용되는 채널화 코드인 orthogonal variable spreding factor(OVSF) 코드의 생성특성을 이용하여 발생된 OVSF 코드를 다중전송률 MC-CDMA의 확산부호로 사용한다. 사용자의 전송률에 따라 길이가 다른 OVSF 코드를 확산부호로 사용하며 OVSF 코드 트리에서 같은 가지에 속한 코드들을 사용하는 사용자들을 모아 그룹화를 한다. 제안된 다중 전송률 비동기 MC-CDMA 시스템을 위한 모델을 제시하길 이에 따른 시스템 성능분석을 행한다. 제안된 시스템과 직교부호를 확산부호로 사용하는 단일 전송률 MC-CDMA시스템의 성능과 비교 분석한다.

• 한국통신학회논문지
• /
• 제27권6B호
• /
• pp.593-600
• /
• 2002

The reverse link signal power required for multimedia traffic in multipath faded single-code (SC-) and multi-code CDMA (MC-CDMA) systems is investigated. The effect of orthogonality loss among multiple spreading code channels is herein characterized by the orthogonality factor. The required signal power in both the CDMA systems is then analyzed in terms of the relative required signal power ratio of data to voice traffic. The effect of varying system parameters including spreading bandwidth, the of orthogonality factor, and the number of spreading codes are examined. Analytical results show that MC-CDMA users transmitting only a single traffic type require significantly more power than SC-CDMA users with only a single traffic type. On the other hand, MC-CDMA users transmitting multimedia traffic require power levels approximately identical to SC-CDMA users with multimedia traffic. The results can be used in the design of radio resource management (e.g., power allocation) scheme for wireless multimedia services.

• 한국미생물·생명공학회지
• /
• 제17권3호
• /
• pp.231-235
• /
• 1989

부착성 동물세포인 recombinant human embryonic kidney cell line 293을 5% FBS가 함유된 DME/F12(3:1) mixture 배지에서 배양할 경우 static culture에서와는 달리 미립담체 배양에서는 낮은 부착효율과 spreading의 저해현상이 관찰되었다. Cell line 293의 미립담체 배양에 있어서 배지내의 serum은 세포의 미립담체에 대한 부착속도(attach-ment rate)를 감소시킬 분만 아니라 세포의 증식을 저해한다는 사실을 확인하였다. 이러한 경우, conditioned microcarrier를 이용함으로써 미립담체로부터 세포의 탈착을 어느 정도 막을 수 있었다. 특히 autocrine growth factor를 생성하는 hepatoma cell line인 HpG 2 cell을 배양하여 얻은 conditioned medium을 serum-free medium에 첨가하여 사용함으로써 세포의 정상적인 성장 분만 아니라 growth-stimulation을 유도할 수 있었다.

• 대한전자공학회:학술대회논문집
• /
• 대한전자공학회 2003년도 하계종합학술대회 논문집 I
• /
• pp.230-233
• /
• 2003

In this paper, it is shown that, in DS/CDMA mobile systems, halving or doubling the spreading factor (HSF or DSE) when retransmission is requested possibly improves the throughput. Given transmit power, DSF essentially decreases probability of packet error (PPE) by increasing the signal energy per information bit. It, however, doubles the time duration needed for transmitting the original packet. On the other hand, HSF increases PPE. It, however halves the time duration required to carry the original packet. Thus, the efficiency of HSF or DSF as a retransmission strategy depends on the amount of increased or reduced PPE after HSF or DSF is selected. With achieving given residual error probability (REP) in CDMA systems, the effective throughput is evaluated in this paper to find conditions with which HSF or DSF achieves better performance than using the original one. Analytic results show that HSF or DSF performs better when relatively small or big changes in their PPE's are present, respectively.

• Molecules and Cells
• /
• 제42권8호
• /
• pp.589-596
• /
• 2019

${\beta}Pix$ is a guanine nucleotide exchange factor for the Rho family small GTPases, Rac1 and Cdc42. It is known to regulate focal adhesion dynamics and cell migration. However, the in vivo role of ${\beta}Pix$ is currently not well understood. Here, we report the production and characterization of ${\beta}Pix$-KO mice. Loss of ${\beta}Pix$ results in embryonic lethality accompanied by abnormal developmental features, such as incomplete neural tube closure, impaired axial rotation, and failure of allantois-chorion fusion. We also generated ${\beta}Pix$-KO mouse embryonic fibroblasts (MEFs) to examine ${\beta}Pix$ function in mouse fibroblasts. ${\beta}Pix$-KO MEFs exhibit decreased Rac1 activity, and defects in cell spreading and platelet-derived growth factor (PDGF)-induced ruffle formation and chemotaxis. The average size of focal adhesions is increased in ${\beta}Pix$-KO MEFs. Interestingly, ${\beta}Pix$-KO MEFs showed increased motility in random migration and rapid wound healing with elevated levels of MLC2 phosphorylation. Taken together, our data demonstrate that ${\beta}Pix$ plays essential roles in early embryonic development, cell spreading, and cell migration in fibroblasts.

• ETRI Journal
• /
• 제45권2호
• /
• pp.213-225
• /
• 2023

Physical layer security (PLS) can improve the security of both terrestrial and nonterrestrial wireless communication networks. This study proposes a simplified framework for nonterrestrial cyclic prefixed orthogonal variable spreading factor (OVSF)-encoded multiple-input and multiple-output nonorthogonal multiple access (NOMA) systems to ensure complete network security. Various useful methods are implemented, where both improved sine map and multiple parameter-weighted-type fractional Fourier transform encryption schemes are combined to investigate the effects of hybrid PLS. In addition, OVSF coding with power domain NOMA for multi-user interference reduction and peak-toaverage power ratio (PAPR) reduction is introduced. The performance of $\frac{1}{2}$-rated convolutional, turbo, and repeat and accumulate channel coding with regularized zero-forcing signal detection for forward error correction and improved bit error rate (BER) are also investigated. Simulation results ratify the pertinence of the proposed system in terms of PLS and BER performance improvement with reasonable PAPR.

• BMB Reports
• /
• 제51권5호
• /
• pp.230-235
• /
• 2018

Bone resorption by multinucleated osteoclasts is a multistep process involving adhesion to the bone matrix, migration to resorption sites, and formation of sealing zones and ruffled borders. Macrophage colony-stimulating factor (M-CSF) and osteopontin (OPN) have been shown to be involved in the bone resorption process by respective activation of integrin ${\alpha}v{\beta}3$ via "inside-out" and "outside-in" signaling. In this study, we investigated the link between signal modulators known to M-CSF- and OPN-induced osteoclast adhesion and spreading. M-CSF- and OPN-induced osteoclast adhesion was achieved via activation of stepwise signals, including integrin ${\alpha}v{\beta}3$, $PLC{\gamma}$, $PKC{\delta}$, and Rac1. Osteoclast spreading induced by M-CSF and OPN was shown to be controlled via sequential activation, consistent with the osteoclast adhesion processes. In contrast to osteoclast adhesion, osteoclast spreading induced by M-CSF and OPN was blocked via activation of $PLC{\gamma}/PKC{\alpha}/RhoA$ signaling. The combined results indicate that osteoclast adhesion and spreading are selectively regulated via $PLC{\gamma}/PKC{\alpha}-PKC{\delta}/RhoA-Rac1$ signaling.

• 수산해양기술연구
• /
• 제50권2호
• /
• pp.176-184
• /
• 2014

Nowadays, consumption of fisheries products is increasing. There are several factors, one of which is a quantitative development through aquaculture. Another factor is an increase qualitative consumption of fish which require that fish be supplied alive. This requires a lot of technical effort to transport the live fish that have low survival rate (c.f. tuna and mackerel) in coastal waters and in the open sea. To develop a towing cage for transporting the live fish, model test in a circulate water channel and simulation by computer tool were carried out. In order to spread vertically, floats were attached at the upper part of the cage, and iron chains attached at the lower part of the cage. For horizontal spreading, kites were attached on the cage. The tension and spreading performance of the cage were measured. The result shows that the tension and reduction ratio of inside volume of the cage were tended to increase with increased towing speeds. The suitable operation condition in towing cage was 1.0 m/s towing speeds with vertical spreading force 8.7 kN, horizontal spreading force 5.6 kN; in this case the reduction ratio of inside volume of the cage was estimated as 25%.