@article{nguyen_lee_dai_2019, title={QR-Decomposition-Aided Tabu Search Detection for Large MIMO Systems}, volume={68}, ISSN={["1939-9359"]}, DOI={10.1109/TVT.2019.2905642}, abstractNote={In the conventional tabu search (TS) detection algorithm for multiple-input multiple-output (MIMO) systems, the cost metrics of all neighboring vectors are computed to determine the best neighbor. This can require an excessively high computational complexity, especially in large MIMO systems because the number of neighboring vectors and the dimension per vector are large. In this study, we propose an improved TS algorithm based on the QR decomposition of the channel matrix (QR-TS), which allows for finding the best neighbor with a significantly lower complexity compared with the conventional TS algorithm. Specifically, QR-TS does not compute all metrics by early rejecting unpromising neighbors, which reduces the computational load of TS without causing any performance loss. To further optimize the QR-TS algorithm, we investigate novel ordering schemes, namely the transmit-ordering (Tx-ordering) and receive-ordering (Rx-ordering), which can considerably reduce the complexity of QR-TS. Simulation results show that QR-TS reduces the complexity approximately by a factor of two compared with the conventional TS. Furthermore, when both Tx-ordering and Rx-ordering are applied, QR-TS requires approximately $60\%\text{ -- }90\%$ less complexity compared with the conventional TS scheme. The proposed algorithms are suitable for both low-order and high-order modulation, and can achieve a significant complexity reduction compared to the Schnorr–Euchner and $K\text{-}$best sphere decoders in large MIMO systems.}, number={5}, journal={IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY}, author={Nguyen, Nhan Thanh and Lee, Kyungchun and Dai, Huaiyu}, year={2019}, month={May}, pages={4857–4870} }
 @article{lee_lee_lee_chong_2012, title={Commoncode: A code-reuse platform for wireless network experimentation}, volume={50}, number={3}, journal={IEEE Communications Magazine}, author={Lee, J. and Lee, J. and Lee, K. and Chong, S.}, year={2012}, pages={156–163} }
 @inproceedings{selvanayagam_wang_jiang_lee_rhee_2012, title={Reducing redundant cross-ISP traffic in peer-to-peer systems via explicit coordination}, DOI={10.1109/ccnc.2012.6181137}, abstractNote={Locality-aware P2P file sharing systems have drawn the attention of the research community as a promising technique to alleviate the tussle between P2P traffic and ISPs. However, existing locality-based schemes mainly focus on how to distinguish whether a peer is local or not and pay less attention to how to utilize the locality information. Typically, they simply bias the peer selection towards local peers in the hope that it will reduce cross-ISP traffic. In this paper, we argue that such coarse-grained control is inadequate and propose a fine-grained mechanism called Swarm-over-Swarm (SOS). Through explicit coordination on piece selection among local peers, SOS is much more effective in reducing redundant cross-ISP traffic than existing schemes. We implement SOS in both NS-2 and a real BitTorrent client and demonstrate the effectiveness of our solution via both simulations and Internet experiments.}, booktitle={2012 ieee consumer communications and networking conference (ccnc)}, author={Selvanayagam, A. H. A. and Wang, Y. G. and Jiang, H. Q. and Lee, K. and Rhee, I.}, year={2012}, pages={603–607} }
 @article{lee_hong_kim_rhee_chong_2012, title={SLAW: Self-Similar Least-Action Human Walk}, volume={20}, ISSN={["1558-2566"]}, DOI={10.1109/tnet.2011.2172984}, abstractNote={Many empirical studies of human walks have reported that there exist fundamental statistical features commonly appearing in mobility traces taken in various mobility settings. These include: 1) heavy-tail flight and pause-time distributions; 2) heterogeneously bounded mobility areas of individuals; and 3) truncated power-law intercontact times. This paper reports two additional such features: a) The destinations of people (or we say waypoints) are dispersed in a self-similar manner; and b) people are more likely to choose a destination closer to its current waypoint. These features are known to be influential to the performance of human-assisted mobility networks. The main contribution of this paper is to present a mobility model called Self-similar Least-Action Walk (SLAW) that can produce synthetic mobility traces containing all the five statistical features in various mobility settings including user-created virtual ones for which no empirical information is available. Creating synthetic traces for virtual environments is important for the performance evaluation of mobile networks as network designers test their networks in many diverse network settings. A performance study of mobile routing protocols on top of synthetic traces created by SLAW shows that SLAW brings out the unique performance features of various routing protocols.}, number={2}, journal={IEEE-ACM TRANSACTIONS ON NETWORKING}, author={Lee, Kyunghan and Hong, Seongik and Kim, Seong Joon and Rhee, Injong and Chong, Song}, year={2012}, month={Apr}, pages={515–529} }
 @inproceedings{lee_kim_chong_rhee_yi_2011, title={Delay-capacity tradeoffs for mobile networks with levy walks and levy flights}, DOI={10.1109/infcom.2011.5935159}, abstractNote={This paper analytically derives the delay-capacity tradeoffs for Lévy mobility: Lévy walks and Lévy flights. Lévy mobility is a random walk with a power-law flight distribution. α is the power-law slope of the distribution and 0 &#60; α ≤ 2. While in Lévy flight, each flight takes a constant flight time, in Lévy walk, it has a constant velocity which incurs strong spatio-temporal correlation as flight time depends on traveling distance. Lévy mobility is of special interest because it is known that Lévy mobility and human mobility share several common features including heavy-tail flight distributions. Humans highly influence the mobility of nodes (smartphones and cars) in real mobile networks as they carry or drive mobile nodes. Understanding the fundamental delay-capacity tradeoffs of Lévy mobility provides important insight into understanding the performance of real mobile networks. However, its power-law nature and strong spatio-temporal correlation make the scaling analysis non-trivial. This is in contrast to other random mobility models including Brownian motion, random waypoint and i.i.d. mobility which are amenable for a Markovian analysis. By exploiting the asymptotic characterization of the joint spatio-temporal probability density functions of Lévy models, the order of critical delay, the minimum delay required to achieve more throughput than Θ(1/√n) where n is the number of nodes in the network, is obtained. The results indicate that in Lévy walk, there is a phase transition that for 0 &#60; α &#60; 1, the critical delay is constantly Θ(n<sup>1/2</sup>) and for 1 ≤ α ≤ 2, is Θ(n<sup>α/2</sup>). In contrast, Lévy flight has critical delay Θ(n<sup>α/</sup>2) for 0 &#60; a ≤ 2.}, booktitle={2011 proceedings ieee infocom}, author={Lee, K. and Kim, Y. and Chong, S. and Rhee, I. and Yi, Y.}, year={2011}, pages={3128–3136} }
 @article{rhee_shin_hong_lee_kim_chong_2011, title={On the Levy-Walk Nature of Human Mobility}, volume={19}, ISSN={["1558-2566"]}, DOI={10.1109/tnet.2011.2120618}, abstractNote={We report that human walks performed in outdoor settings of tens of kilometers resemble a truncated form of Levy walks commonly observed in animals such as monkeys, birds and jackals. Our study is based on about one thousand hours of GPS traces involving 44 volunteers in various outdoor settings including two different college campuses, a metropolitan area, a theme park and a state fair. This paper shows that many statistical features of human walks follow truncated power-law, showing evidence of scale-freedom and do not conform to the central limit theorem. These traits are similar to those of Levy walks. It is conjectured that the truncation, which makes the mobility deviate from pure Levy walks, comes from geographical constraints including walk boundary, physical obstructions and traffic. None of commonly used mobility models for mobile networks captures these properties. Based on these findings, we construct a simple Levy walk mobility model which is versatile enough in emulating diverse statistical patterns of human walks observed in our traces. The model is also used to recreate similar power-law inter-contact time distributions observed in previous human mobility studies. Our network simulation indicates that the Levy walk features are important in characterizing the performance of mobile network routing performance.}, number={3}, journal={IEEE-ACM TRANSACTIONS ON NETWORKING}, author={Rhee, Injong and Shin, Minsu and Hong, Seongik and Lee, Kyunghan and Kim, Seong Joon and Chong, Song}, year={2011}, month={Jun}, pages={630–643} }
 @inproceedings{lee_rhee_lee_yi_chong_2010, title={Mobile data offloading: How much can WiFi deliver?}, volume={40}, number={4}, booktitle={Computer Communication Review}, author={Lee, K. and Rhee, I. and Lee, J. and Yi, Y. and Chong, S.}, year={2010}, pages={425–426} }