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A Novel Random Access for Fixed-Location Machine-to-Machine Communications in OFDMA Based Systems
Kab Seok Ko,Min Jeong Kim,Kuk Yeol Bae,Dan Keun Sung,Jae Heung Kim,Jae Young Ahn IEEE 2012 IEEE communications letters Vol.16 No.9
<P>Machine-to-machine (M2M) communications typically exhibit features such as a large number of devices, low data-rates, small-sized packets, and low or no mobility, while human-to-human (H2H) communications typically support a small number of users, high data-rates, large-sized packets, and high mobility. To support M2M communications in future cellular systems, one of the most challenging problems is to resolve a collision problem in random access because of access attempts from a large number of devices. For a large class of fixed-location M2M services such as smart metering and remote sensing, each machine device has fixed uplink timing alignment (TA) due to a fixed distance between the machine device and its eNodeB. We propose a novel random access scheme based on its fixed TA information for M2M communications at a large number of fixed-location machine devices in future orthogonal frequency division multiple access (OFDMA)-based cellular systems like Long Term Evolution (LTE) system. The proposed random access scheme yields significantly lower collision probability, shorter access delay, and higher energy-efficiency, compared with the conventional random access scheme.</P>
Ko, Kab Seok,Jung, Bang Chul,Hoh, Mijeong IEEE 2018 IEEE COMMUNICATIONS LETTERS Vol.22 No.4
<P>In this letter, we propose a distributed interference alignment (DIA) technique in a two-cell multiple-input multiple-output (MIMO) network with dynamic time division duplex (TDD) mode under local channel state information assumption. The dynamic TDD operation introduces new types of interference, such as downlink-to-uplink [base station to base station (BS–BS)] and uplink-to-downlink [mobile station to mobile station (MS–MS)] interferences. Under the assumption of rank-deficient BS–BS MIMO interference channel, we mathematically characterize the achievable degrees-of-freedom of the proposed DIA technique for a given number of antennas at BS/MS. Through extensive computer simulations, it is shown that the proposed DIA technique outperforms the conventional techniques in terms of sum-rate at the cost of signaling overheads for the BS–BS and MS–MS channel overhearing.</P>
Achievable Rate Analysis of Opportunistic Transmission in Bursty Interference Networks
Nam, Hyunwoo,Ko, Kab Seok,Bang, Inkyu,Jung, Bang Chul IEEE 2018 IEEE communications letters Vol.22 No.3
<P>In this letter, we consider the <TEX>$K$</TEX>-user <I>bursty</I> fading interference channel, where each user transmits data intermittently with a certain probability under the <I>local</I> channel state information assumption. In particular, we consider three different transmission techniques with fixed power: random transmission (RT), opportunistic transmission-based on generating interference (OT-1), and opportunistic transmission based on desired channel gain (OT-2). We mathematically analyze the <I>average</I> achievable rates of the three transmission techniques, which is the first theoretical result to the best our knowledge. The analysis is validated via extensive computer simulations. It is shown that the opportunistic transmission techniques (OT-1 and OT-2) result in better performance in terms of the achievable rate compared with the RT as well as the conventional non-bursty transmission technique.</P>
천병식(Chun Byung-Sik),고갑수(Ko Kab-Soo),장은석(Chang Eun-Seok),임지섭(Lim Ji-Sub),이용한(Lee Yong-Han) 한국철도학회 1999 한국철도학회 학술발표대회논문집 Vol.- No.-
This paper is a study on the improvement effects by quick lime pile through theoretical analysis and in-situ construction test. Effects of strength increase is studied to verify the improvement effects of soft ground arounding quick lime pile. First, engineering characteristics of quick lime and ground was studied, in the second place, laboratory test(consolidation test, triaxial compression test) and in-situ test(portable cone penetration test, vane test) were performed for verification of strength increase of adjacent ground. Finally, the results of in-situ test were compared with those of theorecal study. From in-situ test results, strength at 28th curing days(6.11~6.55t/㎡) was twice as great as strength before improvement(3.06t/㎡) and was slightly greater than theoretical value(4.95t/㎡).