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길계태,이주용,김훈,조동호 한국통신학회 2021 Journal of communications and networks Vol.23 No.2
This paper compares the uniform circular array based or bital angular momentum (UCA-OAM) scheme, which enables spa tial multiplexing transmission of data symbols via multiple OAMmodes, with the UCA-MIMO scheme through numerical analysisand simulation in terms of spectral efficiency and feedback over head. Specifically, based on the relations between the eigenmodesof the UCA-SVD-MIMO system and the modes of UCA-OAM sys tem as well as the capacity formula, the channel capacities of thetwo systems are compared for the cases where equal power alloca tion and waterfilling power allocation are employed, and then theeffectiveness of the analytical results are verified through simula tion.
FLC-C VDSL 선로특성과 Coverage에 관한 연구
길계태,하종영,권순철,한권훈,신종원,임종대 한국통신학회 2000 韓國通信學會論文誌 Vol.25 No.3
In this paper, we analyzed the reach performance of the FLC-C VDSL system using 4-CAP modulation scheme. We measured the attenuation of VDSL lines and their noise characteristics, and calculated the channel capacity. And then, we evaluated the VDSL coverage fro each type of cables; CPEV 0.5mm, CPEV 0.65mm, UTP3 0.5mm, UTP5 0.5mm, FS 0.4mm, FS 0.5mm. In case that FLC-C VDSL modern transmits 25.92 Mbps data over a UTP5 0.5mm cable, the VDSL reach appears to be about 570mm.
SER/BER Analysis for 2-by-N MIMO-STBC Systems in Rayleigh Fading Channels
길계태,이성춘,현광민,Gil, Gye-Tae,Lee, Seong-Choon,Hyun, Kwang-Min The Korean Institute of Communications and Informa 2010 韓國通信學會論文誌 Vol.35 No.6c
In this paper, novel approximated closed-form expressions of the SER(Symbol Error Rate) and BER(Bit Error Rate) are presented for the multi-input multi-output space-time block coding(MIMO-STBC) system employing two transmit and N receive antenna(s) in Rayleigh fading channels. Assuming a zero-forcing equalizer and a single-symbol maximum-likelihood (ML) decoder, the formulas are derived for the SER and BER, and then their approximated counterparts are also derived. In the derivation of the approximated expressions, acurve-fitting model is adopted that can eliminate the integral operators in the exact expressions.
길계태,은종관,박영철,이상철 한국통신학회 1991 韓國通信學會論文誌 Vol.16 No.11
Flooding is known to be an effective routing mechanism not only in circuit switched networks but also packet switched networks since it minimizes the time required for up calls and does not have to maintain routing tables or distance tables by periodically intercommunicating among all the network nodes. However, one main drawback of it is the overhead on the control message signaling channels, In the paper, we propose an overlaying scheme on the existing mechanism that retains the desired properties of flooding, yet provides congestion control to the network. This is done by utilizing the wasted search messages to inform the network of the conditions of each path from one node to another. The overhead is to maintain a path table in each node. However, this overhead is not so critical. Also, this scheme can take advantages further by limiting the extent of message propagation through the network and by incorporating trunk reservation schemes additionally. 본 논문에서는 근사 포화형 경로 절정 알고리즘을 제안한다. 이 방식의 주 Idea는 flooding 되어 망의 경계로 소멸해가는 search message들을 이용하여 각 노드의 path table을 갱신함으로써 각 노드가 이 정보를 가지고 자신에게 도착하는 search message들이 망의 congestion의 증가가 가장 작은 path를 선택하게 함으로써 망의 congestion을 control하는 것이다. 이 알고리즘의 유용함을 인지시키고자 회전 교환 망과 패킷 교환 망에서 각각 모의 실험을 하였다. 또한 제안된 알고리즘은 다른 분석적인 알고리즘들과 비교할 때 거의 비슷한 성능을 갖음을 알았다. 이 방식의 overhead는 망의 데이타 베이스 관리부에 부가하는 work load이다. 그러나 이 work load는 알고리즘이 제공하는 효율적인 congestion control로 인하여 충분히 상쇄할 수 있다. 이 알고리즘은 configuration이 자주 변하는 동작인 망에서 뿐만 아니라 일반 상용 망에서도 유용한 것이다.